I'd like some help on the following... I know the answer for the case below, having drawn it in CAD, however I'd like to understand the methodology as to how I can calculate this manually, given some known dimensions/angles.

3000x3000 square base, with two intersecting 25 degree planes. Diagonal between bottom left corner and top right corner appears as being 45 degree, when the 3D shape is viewed in plan.

How do I arrive at the angle of 42.186 degree?, given that the values above and the attached drawing. I assume a triangle/series of triangles will get me there, but I'm stumped

angles.jpg

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