(d) The work done in a $PV$ diagram is the area enclosed.
The work done $= \frac{1}{2}\left( 3V_{1} - V_{1} \right).(4P_{1} - P_{1})$
$\Rightarrow W = - 3P_{1}V_{1}$. If the direction of change is clockwise it is positive. Since here it is anticlockwise, work done is negative