I'm aware that this is a very basic question, but I can't seem to find the right terms to Google for. Any guidance would be appreciated.

What I want is a rectangular box with a triangular piece removed from it. The angle of the triangle being removed should be a specific angle.

What I've tried:

- Draw a square
- Pop that out into 3d
- Draw a line on one of the six sides of the box
- Push that line into the box using the Move tool

This gives me the shape I want, but without the exact control over the angle I need.

I've also tried using the Rotate tool on the line drawn in Step 3 above, and while that gives very interesting results, none of them is what I need.

My last resort will probably be a roundabout way of doing this, by building one half of the shape, and mirroring it - but that doesn't seem very proper either. Any suggestions?