need a starting point urgently.

A manufacturer is to design and make plastic drinking cups in the form of an open cylinder and decides that the maximum capacity of the cups must be 400cm^3. clearly the manufacturer wishes to keep costs to a minimum. what dimensions for the cylinder would you suggest?

any help would be appreciated on this i have to give a presentation on it on thursday and have been struggling with it for weeks. i don't even know where to start from all i've got is the formula for the area of a cylinder.

i've tried a trial and error but it's not really what they're looking for and i don't think i was any closer to the answer anyway.

(Sweating)