The torque about centre is $\tau =I \alpha$, here $I$ is the moment of inertia and $\alpha$ is angular acceleration.

The formula of moment of inertia is $M{R}^2$.

$F\times R=M{R}^2\alpha$

$30\times 0.4=3\times {\left(0.4\right)}^2\alpha$

$12=3\times 0.16\alpha$

$400=16\alpha$

Thus, angular acceleration is $\alpha =25\mathrm{ rad}/{\mathrm{s}}^2$