Answer
a. $P_A(V_C-V_A)$.
b. $P_C(V_C-V_A)$.
c. $\frac{1}{2}(P_A+P_C)(V_C-V_A)$.
Work Step by Step
The work done is the area under the PV curve that represents the process.
As the process goes from state A to state B, or from state D to state C, there is no work done, because there is no volume change. The PV diagram is provided with the problem.
a. $W_{ADC}=W_{AD}+0=P_A(V_C-V_A)$
b. $W_{ABC}=0+W_{BC}=P_C(V_C-V_A)$
c. To find this area, use the formula for a trapezoid.
$W_{AC}=\frac{1}{2}(P_A+P_C)(V_C-V_A)$