$4-20$ A piston$-$cylinder device contains $0\mathrm{.}15kg$ of air initially

at $2$MPa and $350C.$ The air is first expanded isothermally to

$500$kPa, then compressed polytropically with a polytropic expo$-$

nent of $1\mathrm{.}2$ to the initial pressure, and finally compressed at the

constant pressure to the initial state. Determine the boundary

work for each process and the net work of the cycle.