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'Two Right Angles' printed from https://nrich.maths.org/
Triangles $QPR$ and $RPS$ are similar.
So:$\frac{PR}{PS}=\frac{PQ}{PR}$. Hence $PR^2=PQ\times
PS=\frac{7}{3}\times\frac{48}{7}=16$.
So $PR$ is $4$ units long.