Answer
(a) $\$14.40$
(b) It would take 34.7 months to recover the additional cost.
Work Step by Step
(a) We can find the cost of electricity for 30 days:
$C_e = (\$0.10/kWh)(1.0~kW)(30\times 24~h)(0.20) = \$14.40$
(b) We can find the cost of electricity for 30 days for the more expensive refrigerator:
$C_e = (\$0.10/kWh)(0.80~kW)(30\times 24~h)(0.20) = \$11.52$
We can save $\$2.88$ each month. We can find the number of months it takes to recover the additional cost:
$\frac{\$100}{\$2.88} = 34.7$
It would take 34.7 months to recover the additional cost.