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
