The efficiency $(\eta)=1-\frac{T_{2}}{T_{1}}$ or $\frac{T_{2}}{T_{1}}=1-\eta$
For first case, $\frac{T_{2}}{500}=1-0.4$
$T_{2}=300 K$.
For sewnd case, $\frac{300}{T_{1}}=1-0.5$
$T_{1}=6 00 K .$



$I.$ Area $ABCD =$ Work done on the gas
$II.$ Area $ABCD =$ Net heat absorbed
$III.$ Change in the internal energy in cycle $= 0$
Which of these are correct