As far as I understand your sketch ...

1. The vertex of the pyramid (Obviously you labeled it V) is perpendicularly above the intersection M of the two diagonals of the base area.

The diagonal has a length of 25.

2. The height h, a half diagonal and an edge form a right triangle:

Solve for h.

3. The angle is half as large as the angle . Use the right traingle MCV to determine the angle :