Explanation
UI Automation is a feature that enables you to automate the interaction with UI elements on remote machines using native selectors. To use UI Automation in a scenario where multiple RDP connections are involved, you need to install the UiPath Windows Remote Desktop extension on the client machines and the UiPath Remote Runtime component on the destination machine. The extension allows you to identify UI elements on the remote desktop and send keyboard and mouse events to them. The Remote Runtime component enables the communication between the extension and the UiPath Robot service. In this case, Machine A and Machine B are client machines, while Machine C is the destination machine. Therefore, you need to install the RDP extension on Machine A and Machine B, and the Remote Runtime component on Machine C. (UiPath Studio documentation1) References:
1: About Native RDP Automation - UiPath Studio.

Explanation
Variables can be created from different areas or panels in the UiPath Studio interface, such as the body of an activity, the properties panel, the expression editor, or the variables panel. However, the activities panel is the only one among the given options that is a valid area for creating variables. The activities panel contains a list of activities that can be dragged and dropped to the designer panel to build workflows. By right-clicking a field in an activity and selecting Create Variable from the context menu, or pressing Ctrl+K, a variable can be created and assigned to that field. The variable's type and scope are automatically determined based on the activity and the container it is part of.
References:
Create Variables Tutorial in Studio | UiPath
Studio - Managing Variables - UiPath Documentation Portal
Managing Variables - UiPath Studio

Explanation
The Triggers section of the State activity is used to specify the conditional or trigger logic and multiple outgoing transitions in a state machine. A trigger is a condition that evaluates to true or false and determines whether the state machine should move from one state to another. A transition is a link between two states that defines the direction of the state machine flow. You can add multiple triggers and transitions to a state and configure their properties, such as priority, display name, and action. (UiPath Studio documentation1) References:
1: State - UiPath Activities.

Explanation
The Assign activity is used to assign a value to a variable. In this case, the variable is "qty". The value of the variable will be 80 after executing the Assign activity because the expression in the Assign activity is
"dt.AsEnumerable().Where(Function(x) x("Item").ToString.Equals("mango")).Select(Function(y) y("Quantity")).ToString". This expression is filtering the data table "dt" for rows where the "Item" column is equal to "mango" and then selecting the "Quantity" column from those rows. Since there is only one row in the data table where "Item" is equal to "mango", the value of the "Quantity" column in that row is 80. (UiPath Studio documentation) References:
[Assign - UiPath Activities].

Explanation
The Robotic Enterprise Framework (REF) is a template that provides a structured and consistent way to develop automation processes. The REF uses an Orchestrator queue to store and process the transaction items, which are the units of work for the process. The REF also handles different types of exceptions that may occur during the execution of the process, such as system exceptions and business exceptions. A system exception is an error that prevents the normal execution of the process, such as a network failure or an application crash. A business exception is an error that is related to the business logic or rules of the process, such as an invalid input or an incorrect output. The REF has different mechanisms to deal with these exceptions, such as retrying, logging, and updating the status of the transaction items.
The MaxRetryNumber from the "Config.xlsx" file is a parameter that specifies how many times the REF will retry a transaction item when a system exception occurs. The Max # of retries from the Queue settings from Orchestrator is a parameter that specifies how many times Orchestrator will retry a transaction item when it changes to Failed status due to any exception. These two parameters are independent of each other and have different effects on the retry mechanism.
In this case, the first transaction item throws a business exception, which means that there is something wrong with the data or the logic of the process. The REF will not retry a transaction item when a business exception occurs, because it assumes that retrying will not solve the problem. Instead, the REF will log the exception, update the status of the transaction item to Failed, and move on to the next transaction item. Orchestrator will also not retry a transaction item when it changes to Failed status due to a business exception, because it respects the decision of the REF. Therefore, the transaction will not be retried at all.
References:
1: Robotic Enterprise Framework Template - UiPath Studio.