And nine 50 ohm resistors in parallel is equal to a single 5.55 ohm resistor . E= IR = 0.180A5.55 ohms = 1 V.
Power dissipated by a single 5.55 ohm resistor with 1 V dropped across it is P= IE = 0.180A * 1 V =0.180W = 180mW.
Power dissipated by the 18 leds wired in series parallel with two in each branch is P= IE= 0.180A* 4V =0.720W = 720mW.
Total power dissipated by circuit = 0.72W +0.18W=0.9W = 900mW.