Hello!
For the explanation of this energy conservation exercise, where we'll use energy conservation law, let's see what this principle proposes.
How you should know, mechanical energy conserves in every point, that is to say mechanical energy is same in A point like B point. (Mechanical energy will be represented by "Me")
Once time we know that, let's take the 220 Joules momentum like A point, and when 55 Joules momentum like B point.
Then, let's use the energy conservation principle:
Me(A) = Me(B)
220 J = Me(B)
220 J = Ke + Gpe
220 J = 55 J + Gpe
Gpe = 220 J - 55 J = 165 J
Gravitational potential energy is of One hundred sixty five Joules (165 J).
║Sincerely, ChizuruChan║