Let's get some of these vertices labelled. I'm going to call the 3 "corners" across the top A B C from left to right, and along the bottom diagonal D E F. Additionally I will call the vertical unknown distance x, the leftmost unknown y, and the rightmost unknown z.

Note that trapezoids ACFD and BCFE are similar, so the sides are in proportion to each other.

Thus:

(80 + 120)/120 = 210/z

Solve for z. I get z = 126. Thus y + z = 210 gives y = 84.

Again:

(80 + 120)/120 = 90/x

I get x = 54.

-Dan