One of the possible causes of slow OS performance, random shutdowns, and loud fan noise is the CPU overheating. This can happen due to dust accumulation, faulty cooling system, or high CPU usage. Overheating can damage the CPU and other components, so it is important to monitor the CPU temperature and take preventive measures.
Reference:
The Official CompTIA A+ Core 1 Student Guide (Exam 220-1101) eBook1, page 2-9, section "CPU Cooling Methods".
The Official CompTIA A+ Core 1 (220-1101) Certification Study Guide2, page 2-11, section "Troubleshooting CPUs".

A smartphone that takes more than a day to fully charge may be due to a charger that is not powerful enough. The technician should verify that the charger is rated for the smartphone's battery capacity and that it is providing the correct voltage and amperage123.

The correct answer is D. Default gateway.
A default gateway is the device that connects a local network to other networks, such as the internet. A default gateway is usually a router or a modem that has an IP address on the same subnet as the local network. A default gateway is necessary for a device to communicate with devices outside its local network.
In this case, the user has a self-configured, static IP address of 192.168.1.20, which belongs to the subnet
192.168.1.0/24 (with a subnet mask of 255.255.255.0). However, the default gateway is set to 192.168.0.1, which belongs to a different subnet (192.168.0.0/24). This means that the user's device cannot reach the default gateway, and therefore cannot connect to the internet.
The technician should edit the default gateway to match the correct subnet of the user's device, such as
192.168.1.1 or 192.168.1.254, depending on the configuration of the network.
Reference: CompTIA A+ Core 1 Sample Questions and Study Guide

The technician should check the wattage and the form factor of the power supply to ensure it will support the upgraded workstation. These are the two most important criteria for choosing a compatible and adequate power supply.
* Wattage: The wattage of a power supply is the maximum amount of power it can deliver to the components of the workstation. The wattage of the power supply should match or exceed the total power consumption of the components, especially the new graphics card, which is usually the most power-hungry part. If the power supply does not have enough wattage, it may cause instability, crashes, or damage to the workstation. To estimate the power consumption of the components, the technician can use a power supply calculator tool, such as the ones found in the web search results123. The technician should also add some headroom to the wattage, such as 20% to 50%, to account for peak power consumption, future upgrades, or power supply degradation.
* Form factor: The form factor of a power supply is the physical size and shape of the unit. The form factor of the power supply should fit in the case of the workstation and match the mounting holes and screws. The most common form factor for desktop power supplies is ATX, which measures 150 x 86 x
140 mm. However, some older or smaller workstations may use different form factors, such as SFX, TFX, or FlexATX. The technician should check the specifications of the workstation case and the power supply to ensure they have the same form factor.
Other criteria, such as efficiency rating, heat dissipation, fan type, and modular cabling, are not essential for supporting the upgraded workstation, but they may affect the performance, noise, or aesthetics of the power supply. The efficiency rating is the percentage of input power that is converted to output power, and it indicates how much power is wasted as heat. The heat dissipation is the ability of the power supply to cool itself and prevent overheating. The fan type is the design and size of the fan that cools the power supply, and it affects the noise level and airflow of the unit. The modular cabling is the feature that allows the user to detach unused cables from the power supply, and it helps to reduce clutter and improve airflow inside the case.
References:
* How to Choose the Right Power Supply for Your PC - Lifewire4
* How to Choose a Power Supply: 7 Steps (with Pictures) - wikiHow5
* How to pick the best PC power supply - PCWorld6
* Power Supply Calculator - PSU Wattage Calculator | Newegg1
* Power Supply Calculator | Cooler Master2
* Power Supply Calculator - PSU Calculator | OuterVision3

The correct answers are A. Identify the location of devices that utilize 2.4GHz and D. Map all of the wireless signals in the restaurant. In order to troubleshoot the issue, the technician should first identify the location of devices that utilize the 2.4GHz frequency, as this can cause interference with the wireless signal. Additionally, the technician should map all of the wireless signals in the restaurant in order to identify any potential sources of interference. Checking to see if the phones are IJTP or STP lines, testing to see if the copper electrical wires are causing interference, verifying T568B is being used in the wiring closet patch panel, and scheduling timed router reboots throughout the day are not necessary steps for troubleshooting this issue.