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 $\frac { 2 } { b } g \sin \theta$, where $b$ is $\_\_\_\_$. (Round off to the Nearest Integer)\\
( $g =$ acceleration due to gravity)\\
( $\theta =$ angle as shown in figure)