calculating cost of operation
Hi! last Christmas, I installed 8430 watts (yes, 8.43 kW) of Christmas lights at my mother's house, and would like to pay her for the power used. She pays $0.0751 per kWh, the lights were on 8 hours/night for 50 nights, so I calculated that I owe her $253.24. She claims that I miscalculated, she thinks it can't be that high.
Can someone please tell me, what would the correct price be?