In a $P$-$V$ indicator diagram, the net work done by a gas during a cyclic process is equal to the area enclosed by the cycle. Since the cycle is traced in a clockwise direction, the net work done by the gas is positive. The magnitude of the work done is given by the area of the enclosed figure (a triangle in this standard PYQ). Calculating the area yields $W = \frac{1}{2} \times \Delta P \times \Delta V = 1000\text{ J}$.