Physics-current electricity, circuit

[lydigihome]

Homework Statement

[PLAIN]http://img208.imageshack.us/img208/4577/physicso.jpg

Homework Equations

The Attempt at a Solution

dont know how to do..
help please, how can i find that is 4V?

 

[lydigihome]

oh, some small amendment:
that 15ohm at the top righthand corner should be 10ohm

 

[gneill]

oh, some small amendment:
that 15ohm at the top righthand corner should be 10ohm

But the resistor in the top right-hand corner is 20 ohms...