The diagram below shows the graph of a function $f$ along with points $P$ and $R$, which lie on the graph. Point $Q$ is chosen so that $\triangle PQR$ is a right triangle. (Click on the graph to display a larger version.)

In terms of $a$, $f$, and $h$, give the lengths of the legs of this right triangle.

$PQ$ has length .

$QR$ has length .