posted by Emily .
Solve for X using the side-splitting theorem for a triangle: upper left= 6x-10, upper right= 5x, lower left= 4x+8, lower right=4x
set up the proportion
(6x-10)/(4x+8) = 5x/(4x)
the x's on the right side will cancel, then cross-multiply, it solves very nicely
I had x = 20