Shaft $\left(1\right)$ has a diameter of $0.75 \mathrm{in}.$ and shaft $\left(2\right)$ has a diameter of $1.25 \mathrm{in}.$ The polar moments of inertia for the two shafts are thus:

$$\begin{gathered} {\mathrm{J}}_1=\frac{\mathrm{\pi }}{32}{{\mathrm{d}}_1}^4=\frac{\mathrm{\pi }}{32}{\left(0.75 \mathrm{in}.\right)}^4=0.031063 \mathrm{in}{.}^4 \\ {\mathrm{J}}_2=\frac{\mathrm{\pi }}{32}{{\mathrm{d}}_2}^4=\frac{\mathrm{\pi }}{32}{\left(1.25 \mathrm{in}.\right)}^4=0.239684 \mathrm{in}{.}^4 \end{gathered}$$