$\mathrm{TV}^{\gamma -1}=$ constant $\Rightarrow \mathrm{T}_{1}(5.6)^{2 / 3}=\mathrm{T}_{2}(0.7)^{2 / 3}$
$\Rightarrow \mathrm{T}_{1}(8)^{2 / 3}=\mathrm{T}_{2} \Rightarrow 4 \mathrm{T}_{1}=\mathrm{T}_{2}$
$\mathrm{W}_{\mathrm{gas}}=\frac{-n R \Delta T}{\gamma-1}=-\frac{(1) R\left(3 T_{1}\right) \times 3}{4 \times 2}=-\frac{9}{8} R T_{1}$
Therefore $\mathrm{W}_{\text {external}}=\frac{9}{8} R T_{1}$


