A solid disc of radius a and mass m rolls down without slipping on...

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 $\dfrac{2}{b}gsin\theta$, where $b$ is _______. (Round off to the Nearest Integer)

($g =$ acceleration due to gravity)

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