PROBLEM $2[4$ points$]$

LE light bulbs typically cost $$3\mathrm{.}50,$ have a life span of $9$ years, and use about $$1\mathrm{.}60$ of

electricity a year. CE light bulbs cost $$0\mathrm{.}50$ but they last only about a year and use about

$$6\mathrm{.}60$ of energy. If the real discount rate is $5\%,$ decide which lightbulb is a better purchase

with respect to their total annual cost.