Answer
See the detailed answer below.
Work Step by Step
For the fluorescent bulb, the cost of 10,000 h is given by
$${\rm Cost}_{\rm fluorescent }=\$ 5+(0.015){\rm kW}\cdot (0.10){\rm\$ /kW\;h}\cdot (10,000)\;\rm h$$
where $\$ 5$ is the price of one fluorescent bulb.
Thus,
$${\rm Cost}_{\rm fluorescent }=\$\color{red}{\bf 20} $$
For the ordinary incandescent bulb, the cost of 10,000 h means we need 10 bulbs since the one remains working for only 1000 h.
Thus,
$${\rm Cost}_{\rm incandescent }=(\$ 0.5)(10)+(0.060){\rm kW}\cdot (0.10){\rm\$ /kW\;h}\cdot (1000)\;\rm h$$
where $\$ 0.5$ is the price of one incandescent bulb.
Thus,
$${\rm Cost}_{\rm incandescent }=\$\color{red}{\bf 65} $$
So we had to use the fluorescent bulb.
