In the figure below, segment CD is parallel to segment EF, DE is a transversal, then angles DIH and HGI are congruent as alternate interior angles when two parallel lines are cut by a transversal.
Consider triangles DIH and EGH. In these triangles,
My reasonable estimate might be about 2 1/2 feet. I know that because taking three rulers up to your bedroom or a normal room and get about 2 or 2 1/2 feet