The best security measure to implement when removing a computer from a cubicle is to remove the employee's network access. This will prevent the employee from accessing any network resources or data from the computer, as well as prevent any unauthorized users from using the computer to access the network.
Removing the employee's network access can be done by deleting or disabling the user account, revoking the credentials, or changing the permissions.
The other options are not as effective or necessary as removing the employee's network access. They are:
*Disabling DHCP on the computer being removed will prevent the computer from obtaining an IP address from the network, but it will not prevent the computer from using a static IP address or accessing the network through another device.
*Placing the switch port in a private VLAN will isolate the computer from other devices on the network, but it will not prevent the computer from accessing the network through another port or device.
*Applying a firewall rule to block the computer's IP address will prevent the computer from communicating with the network, but it will not prevent the computer from changing its IP address or accessing the network through another device.
References
1: CompTIA Network+ N10-008 Cert Guide - O'Reilly Media
2: Network+ (Plus) Certification | CompTIA IT Certifications
3: 10 Ways to Secure Office Workstations - Computer Security

A helper address is an IP address that is configured on a router interface to forward DHCP broadcast messages to a DHCP server on another LAN. A DHCP broadcast message is a message that a workstation sends when it needs to obtain an IP address from a DHCP server. Since broadcast messages are not routed across different networks, a helper address is needed to relay the DHCP broadcast message to the DHCP server on another network. References: https://www.comptia.org/training/books/network-n10-008-study-guide (page 199)

Explanation
According to the network troubleshooting methodology, the first step is to identify the problem and gather information about the current state of the network using the network troubleshooting tools that are available1. The next step is to determine if anything has changed in the network configuration, environment, or usage that could have caused or contributed to the performance issues1. This step helps to narrow down the possible causes and eliminate irrelevant factors. For example, the network administrator could check if there were any recent updates, patches, or modifications to the fileshare server or the network devices that connect to it. They could also check if there was an increase in network traffic or demand for the fileshare server resources2.
The other options are not correct because they are not the next steps in the network troubleshooting methodology. Implementing a fix to resolve the connectivity issues (A) is premature without determining the root cause of the problem. Establishing a theory of probable cause is a later step that requires testing and verification. Documenting all findings, actions, and lessons learned (D) is the final step that should be done after resolving the problem and restoring normal network operations1.

The false camera is seen by people. They think it is real and this prevents them from doing something wrong.