The intersections of 12th St., Constitutional Ave., and Pennsylvania Ave. in Washington, D.C. form a triangle. The Old Post Office is wedged in the 12th St. − Pennsylvania Ave. angle of this triangle. If the 12th St. − Constitutional Ave. angle measures 90°, and the Constitutional Ave. − Pennsylvania Ave. angle measures 30°, what is the measure of the angle the Old Post Office is wedged in?
