NMTC 2014(Junior level)

Geometry Level 3

In the given figure, $PQ=42\text{ cm}$ . $QR$ is the tangent to the semicircle at $Q$ . If the difference of the areas of region $A$ and $B$ is $357\text{ cm}^2$ , then the base $QR$ of the right triangle $PQR$ is (in cm)(Take $\pi=\frac{22}{7}$ )

Note: This problem has appeared in nmtc 2014 junior level.