$5\mathrm{.}74$ To maintain a dwelling steadily at $68F$ on a day when the outside temperature is $32F,$ heating must be provided at an average rate of $700Bt\frac{u}{m}in.$ Compare the electrical power required, in kW $,$ to deliver the heating using $($a$)$ electrical$-$resistance heating, $($b$)$ a heat pump whose coefficient of performance is $3\mathrm{.}5,($c$)$ a reversible heat pump operating between hot and cold reservoirs at $68F$ and $32F,$ respectively.