Seven 40W lamps = 7 × 40 = 280W Five 80W lamps = 5 × 80 = 400W Total power = 280W + 400W = 680W = 680KW1000 = 0.68KW The kilowatt hour = 0.68 KW × 12 hrs = 8.16 KWh Cost is N 7 per KWh So the cost of running them = 8.16KWh × N 7/KWh = 57.12
