i don't get circuits

[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 Vc = R3*(I1 + Is). 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!