double battery circuit

lil_angel_007

1. The problem statement, all variables and given/known data

I have this circuit:
http://img59.imageshack.us/i/doublebattery.png/

2. Relevant equations

what are the currents I1, I2, and I3
and the power being delivered on each resistor

3. The attempt at a solution
i've tried doing 3 equations using the kirchhoff rules but i end up with the wrong answer...my equations were
21 - I1R1 - I3R = 0
15 - I2R2 - I3R = 0
I3 = I1 + I2
what am i doing wrong?

gneill

Must be a problem with your algebra. Your equations appear to be set up okay.