Power = voltage * current, so you need to know the voltage across each resistor and the current flowing through it.
Having worked out the total current delivered by the battery you can calculate the voltage at the point where R1 R2 and R3 join, which is 30V minus the R1 voltage drop.
You can then work out the total current through R3-R6, which will give you the voltage drop across R3 and the voltage at the point where R3 R4 and R5 join.
From that you can then work out the current through R4-6.
So you now know the current through each resistor and through Ohm's Law the voltage across each, from which you can then calculate the power dissipated by each resistor.
Or you could use current loop analysis and solve the whole lot at once with a bunch of simultaneous equations.