A rolling wheel of \( 12 \, \text{kg} \) is on an inclined plane at position \( P \) and connected to a mass of \( 3 \, \text{kg} \) through a string of fixed length and pulley as shown in figure. Consider \( PR \) as friction free surface. The velocity of centre of a mass of the wheel when it reaches at the bottom \( Q \) of the inclined plane \( PQ \) will be \( \frac{1}{2} \sqrt{x g h} \, \text{m} / \text{s} \). The value of \( x \) is ________.
