How Do You Calculate the Voltage Across v1 Using KCL and KVL?

[planauts]

Homework Statement

Find the voltage across v1 in the circuit below:

http://puu.sh/1eD2R

Homework Equations

The Attempt at a Solution

I tried using KVL across loop 1 (from left) and then:
LOOP2: v1, 2ohms,1ohm,4V
LOOP3: also: 5V, 2ohms, 1ohm, 4V

I seem to be getting 3V as the voltage across v1. I don't think I am right because it's not one of the options. The options are:

a) 9 V
b) -9 V
c) -5 V
d) 4 V

My rough work, (if you can decipher my penmanship - near the end, I skipped a steps and just did it in my head/calculator's memory):

Spoiler

http://puu.sh/1eD7L

Also, is it possible to use the loop with the 3A current source to do KVL? I thought it wasn't allowed because I don't know the voltage drop across the current source.

Thanks!

 

[NascentOxygen]

You do know the voltage across the current source. It's 4V minus the drop across that right-most 2Ω resistor (that has 3A through it).

But a simpler way of looking at this is to say the voltage between the top and bottom horiz wires (on your left) is 4V minus the drop across the 1Ω (with 3A in it).