(a) Power of bulb is 100 W, converting this into kW.
Thus,
The bulb is used for 6 hours per day for a year, in 1 year there are 365 days thus, total hours will be:
Electricity used will depend on power and number of hours as follows:
The cost of electricity is $0.15 per kW.h thus, cost of electricity for 219 kW.h will be:
Therefore, annual cost of incandescent light bulb is
(b) Power of bulb is 25 W, converting this into kW.
Thus,
The bulb is used for 6 hours per day for a year, in 1 year there are 365 days thus, total hours will be:
Electricity used will depend on power and number of hours as follows:
The cost of electricity is $0.15 per kW.h thus, cost of electricity for 54.75 kW.h will be:
Therefore, annual cost of fluorescent bulb is .