Answer
The height the student falls is $6.7m$.
Work Step by Step
1) Find the speed of the student just before he hit the ground.
Taking the speed of the student just before he hit the ground as the initial speed $v_0$, we examine the change in speed as he contacts the ground, $$\sum\vec{\overline F}\Delta t=m\vec{v}_f-m\vec{v}_0$$
We have $\vec{v_f}=0m/s$, so the average force exerted by the ground is $\vec{\overline F}=+18000N$; $m=63kg$ and $\Delta t=0.04s$. Therefore, we have $$\vec{v_0}=\frac{m\vec{v}_f-\vec{\overline F}\Delta t}{m}=-11.43m/s$$ $$v_0=11.43m/s$$
2) Apply an equation of kinematics to find the height the student falls
Take $v_0=0, v_f=11.43m/s, g=9.8m/s$ $$v_f^2=v_0^2+2gs$$ $$s=\frac{v_f^2-v_0^2}{2g}=6.7m$$
