0.80 mol of a monatomic ideal gas goes from A to C in two steps…

Isothermal: $\Delta U = 0$, $Q = W = nRT\ln\dfrac{V_2}{V_1}$. Isobaric: $W = p\,\Delta V = nR\,\Delta T$, $Q = nC_p\,\Delta T$. Isochoric: $W = 0$, $Q = \Delta U = nC_v\,\Delta T$.

Molar heat capacities: $C_v = \tfrac{f}{2}R$ and $C_p = C_v + R$ (Mayer), with $\gamma = \dfrac{C_p}{C_v}$. Monatomic: $12.5\ \text{J mol}^{-1}\text{K}^{-1}$, $20.8\ \text{J mol}^{-1}\text{K}^{-1}$, $\gamma = 1.67$. Diatomic: $20.8\ \text{J mol}^{-1}\text{K}^{-1}$, $29.1\ \text{J mol}^{-1}\text{K}^{-1}$, $\gamma = 1.40$. $Q = nC\,\Delta T$, and $\Delta U = nC_v\,\Delta T$ in every process.