Physics Midterm Explanation Kirkoff Rule

[Nimmy]

Its the part c question...which states

C) Suppose we made V = 0. Find the new current running through the 5.00 ohm resistor.So I just took the biggest loop and did it this way

Sum of V = 0

So starting at the upper left hand corner of the circuit

-3A(15 Ohms) + 50 V + I (5) = 0

-45 + 50 +5I = 0

5 +5I = 0
I = -1 A

Which is not correct. The answer I think is supposed to be 2.5 Amps but can you tell me what mistake I'm making here.

 

[Doc Al]

I assume the currents labeled in the diagram are from an earlier part of the problem. You can't just assume that the currents remain the same.