Question: how much power is being dissipated by one of the 10 ohm resistors?
Answer: It is very simple. The 10 ohms resistor connected across a 12 volts battery dissipates the power of 1.44 A² X 10 ohm = 14.4 watts. When an additional 30 ohms is added in series to the existing 10 ohms the power dissipated will be equal to 144 v²/40 ohms = 14.4 watts/4 = 3.6 watts.