What are the current and power equations for a double battery circuit?

[lil_angel_007]

Homework Statement

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

Homework Equations

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

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.