P-V diagram of an ideal gas is as shown in the figure. Work done by the gas in the process ABCD is

${\mathrm{W}}_{\mathrm{AB}} = -{\mathrm{P}}_0{\mathrm{V}}_0$

             ${\mathrm{W}}_{\mathrm{BC}} = 0$

and   ${\mathrm{W}}_{\mathrm{CD}} = 4{\mathrm{P}}_0{\mathrm{V}}_0$

$\therefore {\mathrm{W}}_{\mathrm{ABCD}} = -{\mathrm{P}}_0{\mathrm{V}}_0 +0+4{\mathrm{P}}_{\mathrm{o}}{\mathrm{V}}_{\mathrm{o}}$

                   = 3${\mathrm{P}}_0{\mathrm{V}}_0$