Area of a trapezoid formula:
A = 1/2(Base1 + Base2)*height
I will assume that WX and YZ are the two bases, since that's the only thing that logically makes sense to answer the question.
Plug in what we know
I believe the Area is meant to be 144 unit^2, as no area is ever given as 144^2
144 = 1/2(18 + 18) * h
solve for h
144 = 18 * h
h = 144/18
h = 8
The height is 8.