A solid disc of radius a and mass m rolls down without slipping on an inclined plane making an angle θ…

A solid disc of radius $a$ and mass $m$ rolls down without slipping on an inclined plane making an angle $\theta$ with the horizontal. The acceleration of the disc will be $\frac{2}{\mathit{ }b}g\sin \theta$, where $b$ is _______.  (Round off to the Nearest Integer)

($g=$ acceleration due to gravity)

($\theta =$ angle as shown in figure)