$\left|QR\right|=3\cdot 4\sqrt{13}=12\sqrt{13}$

$P=\frac{24\cdot 36}{2}$

$P=\frac{12\sqrt{13}\cdot h}{2}$

$\frac{24\cdot 36}{2}=\frac{12\sqrt{13}\cdot h}{2}$

$864=12\sqrt{13}\cdot h$

$h=\frac{864}{12\sqrt{13}}=\frac{72}{\sqrt{13}}$

$h=\frac{72}{\sqrt{13}}\cdot \frac{\sqrt{13}}{\sqrt{13}}=\frac{72\sqrt{13}}{13}$