In a cyclic process work done is equal to the area under the cycle and is positive if the cycle is clockwise and negative if anticlockwise.
As is clear from figure, WAEDA=+ Area of △AED=+21P0V0 WBCEB=− Area of △BCE=−21P0V0
The net work done by the system is Wnet =WAEDA+WBCEB =+21P0V0−21P0V0= zero