Struggling with this. Can you help?

Unclear without more information

Explanation:

This is about transfer of energy. If you assume there is no energy lost to the environment (virtually impossible) - then all of the potential energy at the beginning would be transferred to kinetic energy along the route.

So, assuming that the rollercoaster has a velocity of 0 m/s at point A, then you can calculate the potential energy using:

At the point D, you would assume that the energy is split between some kinetic energy and some potential energy. So, we could say that the total energy is the sum of these:

If we assume all energy is transferred (ie. no energy lost to friction/heat etc) then we can equate these two and solve:

However, this answer seems unlikely given the drawing - which implies that there is perhaps more information that is missing??