To find the annual cost, you need to determine the lamp post daily electricity then convert it into years. Assuming a year is 365 days, the calculation would be: 7 hr/day * 365day/year *100 watt= 255500 watt hour.
Before next calculation, you need to know that kWh mean kilo watt hour which means it was 1000 watt hour. Then the calculation of the costs would be:
255500 watt hour * $0.13 / 1000watt hour= $33,215
