compare life time cost: $-$Price of a $60$W incandescent bulb $=$ $$\mathrm{.}75$

$-$An incandescent bulb lasts two years $=2,000$ hours of use

$-$The LED bulb costs $$7\mathrm{.}00/$year in electricity

$-$The $60$W$-$equivalent LED bulb $=$ $$13$

$-$ The LED bulb lasts twenty years $=20,000$ hours of use

$-$The LED bulb costs $$1\mathrm{.}10/$year in electricity

$-$ National average electricity cost $=$ $$9\mathrm{.}90$