Question

The trapezoid in the figure has equal nonparallel sides. The upper base is 6, the lower base is 16, and the diagonal is 12. What is the altitude of the trapezoid?

Answer 1

 draw the figure first (label everything you know). 
add two altitudes, from the endpoints of the top base 
you know that the bottom base is now divided 5-6-5 
using that and the diagonal, pythagorean theorm can be used to find the altitude: 
(c^2)-(a^2)=(b^2) 
(12^2)-(11^2)=b^2 
b^2=23 
altitude is about 4.8