A thermodynamic system is taken through the cyclic PQRSP process. The net work done by the system is

Work done by the system = area of shaded portion on P-V diagram.

  $=(300-100){10}^{-6}\times (200-100)\times {10}^3=20\mathrm{J}$

And direction of process is anticlockwise so work done will be negative, i.e. , $\mathrm{\Delta W}=-20\mathrm{J}$