The correct option is (a) 21.5kJ
For explanation I would say: The current in the circuit is equal to the current in the 5 ohm resistor since it a series connected circuit, hence I=220/(5+10)=14.67A. P=I^2R = 14.67^2*5=1075.8W. E=Pt = 1075.8*20 = 21516J=21.5kJ.