There are two ways to rotate something by giving a specific angle:
first method: hotkey
- click on the object
- click on R
- click on Z, or Y or X, on the basis of the fixed axis you want to keep
- a new window will appear in the bottom left
second method: graphic
- click on the object
- click on the rotating tool on the left
- click on one of the axis, on the basis of the fixed axis you want to keep, without moving the object
- always the same window will appear in the bottom left
