It is desired to compress $1000 \mathrm{scfm}$ of air from $1 \mathrm{~atm}$ and $70^{\circ} \mathrm{F}$ to $10 \mathrm{~atm}$. Calculate the total horsepower required if the compressor efficiency is $80 %$ for

(a) Isothermal compression.

(b) Adiabatic single-stage compression.

(c) Adiabatic three-stage compression with interstage cooling to $70^{\circ} \mathrm{F}$ and optimum interstage pressures.

(d) Calculate the gas exit temperature for cases (b) and (c).

Note: $C_{P}=7 \mathrm{Btu} /\left(\mathrm{lbmol}^{\circ} \mathrm{F}\right)$; Assume ideal gas.