So I did manage to solve my circuit with the voltage source. But I have an issue calculating what happens when I have the current source in order to get the result that the multimeter gives on the screen. Can someone please explain the calculations that I need to do? Thanks in advance for your time.

 

There's no way to tell you what you did wrong in calculating the case for the current source unless you show your best effort to do so.

There are multiple ways to analyze the circuit. Which ones have you tried? What results did you get?

The value shown by the meter is correct.