So I have this one problem:

A wall is being supported by a beam passing over a dumpster 5 feet high and 4 feet from the wall. Find the length of the shortest possible beam.

I know that you need to use similar triangles, but besides that I don't really know what to do. Please Help!!!!!!!!!

This is what I have figured out:

from the ground to the beam (along the wall) is v, and from the dumpster to the beam is v-5

from the wall to the beam (along the ground) is u, and from the dumpster to the beam is u-4.

the beam is x.

I've got it all into one equation: x^2 = v^2 + (20+4)^2

(that's 20 over v-5) (v-5)

I'm stuck now. PLEASE PLEASE PLEASE HELP!!!!!!!!!!!!!!!!!