Q. A man starts walking from the point $P (-3,4)$, touches the $x$-axis at $R$, and then turns to reach at the point $Q (0,2)$. The man is walking at a constant speed. If the man reaches the point $Q$ in the minimum time, then $50\left(( PR )^{2}+( RQ )^{2}\right)$ is equal to ____
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