In a certain city, electricity costs $0.15 per kw·h. what is the annual cost for electricity to power a lamp-post for 7.00 hours per day

Given that the lamp-post is powered for 7 hours per day, thus in a year of 365 days, the lamp post must have been powered for 365 x 7 = 2,555 hours.

Assuming the power rating of the lamp-post is 100 watt.

Then, the energy consumption of the lamp-post is given by 100 x 2,555 = 255,500 watt hour.

But 1,000 watt hour makes 1 kilowatt hour,
thus the energy consumption is 255,500 / 1,000 = 255.5 kw h.

Given that the cost of electricity is $0.15 per kw h, therefore, the cost of 255.5 kw h of electricity is given by 255.5 x 0.15 = $38.33 kw h.