Conic Sections and Parametric Equations · Superchallenge problem

Let $F_1$ and $F_2$ be the foci of the hyperbola $\dfrac{x^2}{9}-\dfrac{y^2}{16}=1$, and let $P$ be a point on the hyperbola with $\angle F_1PF_2=90^\circ$. Find $PF_1+PF_2$.