Constructing an angle which is the difference of two given angles with compass and straightedge

(For assistance see www.mathopenref.com/constdiffangles.html)

1. By construction find the difference between the two angles:

2. By construction find the angle P - (A + B). In other words, add angles A and B, then find the difference between that sum and angle P. For adding angles,
see www.mathopenref.com/constaddangles.html