Some stores use an indirect method of observation. The purpose may be for safety (to avoid...

Some stores use an indirect method of observation. The purpose may be for safety (to avoid collisions) or to foil the attempts of would-be shoplifters. In this situation, a mirror (see in the drawing) is placed at the intersection of two aisles as shown. An observer at point P can then see any movement along the indicated aisle. In the sketch, what is the measure of ∠GEF?