Calculating power in a circuit with loops

[lagwagon555]

Homework Statement

http://img33.imageshack.us/img33/1147/question1x.jpg

Homework Equations

V = IR, Sum of currents at junction = 0.

The Attempt at a Solution

Just doing some exam revision, and found this one in my notes. I'm not really sure how to go about it. Using Kirchhoffs rules, you obviously end up with three variables, and can't solve the equations:

10 - 10I(1) - 20I(2) = 0
15 - 20I(2) - 10I(3) = 0

So I don't know how to calculate the current for any loop on the circuit, since they all have two components. Anyone got any pointers? Thanks!

 

[rl.bhat]

Take I(2) = I(1) + I(3) and solve the equations.