How to Find I1 in a Circuit with Multiple Elements

[IKu]

i'm having trouble with a circuit i got for class and was looking for some help... hopefully this is the right place. i can't figure out how to find I1 for this circuit:
https://netfiles.uiuc.edu/ericlin/www/circuit.jpg

if someone could just explain how to find I1 that would be nice. thanks!

 

[jamesrc]

Well, you know the voltage drop across R₁, so why don't you just use Ohm's law? You could do the same for the voltage drop across R₂ if you'd rather. Or you could even look at the bottom loop, where V_c = R₃*(I₁ + I_s). All three will give you the same answer.

 

[IKu]

ahh... that makes a lot more sense than what i was doing... quick question, could Vc ever be greater than Va in a situation like this? thanks for your help!