Maximize volume, minimize surface area (3 dimensions)

I was assigned this single problem as part of a group project my instructor gave us. He says outright that these problems are much harder than what we were already tested on (group projects are due *after *the test) and we will need to seek extra help outside of class as a way to expand on current knowledge. Could anybody point me in the right direction, or maybe get the problem set-up for me to compute?

*"2. A trash bin with no lid has five sides and is in the shape of a trapezoidal prism as shown in the figure below. If the volume of the bin is to be 16.0 m^3, determine the values of a,b, and c which minimize the surface area."*

http://farm5.static.flickr.com/4037/...b76746e0_o.jpg

Thanks so much for any help!

Dylan