Ok, here is how I think this problems should work. (disclaimer...I'm occasionally wrong, altho this is a rare thing-unfortunatly it happens)
Ok, with the given info (which I'm not gonna restate) prove AB=DC
Statement ---> Proof (thm to back it up)
1. FB = GC ---> Given info
2. Angle FBA and angle GCD
are 90* and equal ---> Given info. (and I don't know you could
put something about perpendicular lines
and 90* angles)
3. Angle AFB = angle DGC ---> Properties of parallel lines...opposite angles
(I think, not corresponding angles)
So... 1=Side 2=Angle 3=Angle AAS
Because of the AAS thm you can say that they are congruent figures and then AB and DC are congruent parts to congruent figures which makes them equal......hope that helps ya.