For shaft $\left(1\right)$:

$$\begin{gathered} {\mathrm{J}}_1=\frac{\mathrm{\pi }}{32}\left({{\mathrm{D}}_1}^4-{{\mathrm{d}}_1}^4\right) \\ =\frac{\mathrm{\pi }}{32}\left[{(50 \mathrm{mm})}^4-{(42 \mathrm{mm})}^4\right] \\ =308,102 {\mathrm{mm}}^4 \end{gathered}$$

and

${\mathrm{c}}_1=\frac{50 \mathrm{mm}}{2}=25 \mathrm{mm}$

For shaft $\left(2\right)$:

$$\begin{gathered} {\mathrm{J}}_2=\frac{\mathrm{\pi }}{32}\left({{\mathrm{D}}_2}^4-{{\mathrm{d}}_2}^4\right) \\ =\frac{\mathrm{\pi }}{32}\left[{(42 \mathrm{mm})}^4-{(30 \mathrm{mm})}^4\right] \\ =225,968 {\mathrm{mm}}^4 \end{gathered}$$

and

${\mathrm{c}}_2=\frac{42 \mathrm{mm}}{2}=21 \mathrm{mm}$