Optimization through derivatives...

Okay, in Calculus, we're doing optimization through the use of derivatives, and I mostly am getting it, but this elusive problem is evading my grasp:

Code:

`Two posts, one 12 feet high and the other 28 feet high, stand 30 feet appart. They are to be statyed by two wires, attached to a single stake, running from ground level to the top of each post. Where should the stake be placed to use the least wire?`

So, I have no clue where to start on this problem. Any ideas? I'm sure it's probably something pathetically simple that'll make me kick myself...