For $1$ mol of ideal gas, a reversible cycle consists of the following:

$$ Starting at T$1=700$ K and P$1=1\mathrm{.}5$ bar, the gas is cooled at constant pressure to T$2=350$ K$.$

$$ From $350$ K and $1\mathrm{.}5$ bar, the gas is compressed isothermally to pressure P$2.$

$$ The gas returns to its initial state along a path for which PT $=$ constant.

What is the thermal efficiency of the cycle? Use CP $=(5/2)$ R and CV $=(3/2)$ R$.$

$($a$)0\mathrm{.}068($b$)0\mathrm{.}248($c$)0\mathrm{.}382($d$)0\mathrm{.}500$