Basic Trig (Angle of Elevation problem)?

First here's my drawing of how I interpret the problem: http://i48.tinypic.com/2nb9087.jpg Q: An airplane is sighted at the same time by two ground observers who are 4 miles apart and both directly west of the airplane. They report the angles of elevation as 10° and 22°. How high is the airplane? I figured the 22 was the person nearest to the aircraft. Can someone please help me? I really don't understand how to solve for the height. Thank you.