If the volume of the triangular prism is 59,85 m3...

The height is 9m, but I’m afraid I can’t explain it well enough for you to be able to solve
a similar problem next period.

First of all, I think the drawing is confusing. You have to take control of your eyes
until they recognize that the dotted lines are in the back, and the solid lines are in
the front.   Then you see that the bottom triangular face of the prism has a base
of 7 and a height of 1.9.  That makes the area of the base (1/2)(b h) = 6.65 m².

The volume of the whole prism is (area of the triangular face) x ’H’ = 59.85.

H = 59.85 / 6.65 = 9 m³.

And the part that’s enough to make you really steamed up is: You don’t need
those measurements of the top face at all. the 3m and 5m on top.