In order to use a kinematic equation, or an energy equation for that matter, we need to know how fast the student was falling just before impact. We can get that number by using the Impulse-Momentum Theorem. As the problem stated, I'm going to use upward as a +y axis.
The final speed of the student is 0 m/s, so
So: , , and .
Note that your will be negative. This is because + is upward and the velocity just before impact is downward. (This is a good check to see if our equation is right.)
Once you get you can either do a work-energy or kinematics problem to determine the height.