During an expansion process of a closed system, the pressure of a gas changes from 100 kPa to 400 kPa according to the following relation: P = a + bV Where “a” is a constant, “b” = 100 kPa/m3, and “V” is the volume of the system in meters cube. If the initial volume of the system is 0.5 m3, calculate the work done by the system during the process and also plot the P – v diagram for the process.