rotational mechanics Questions

The ratio of the radius of gyration of a thin uniform disc about an axis passing through its centre and normal to its plane to the radius of gyration of the disc about its diameter is:

The angular speed of a fly wheel moving with uniform angular acceleration changes from $1200\text{rpm}$ to $3120\text{rpm}$ in $16\text{seconds}$. The angular acceleration in ${\text{rad/s}}^2$ is: