Hmm, you know what's weird. The solution is seven of the first item on the menu.
Since this was obviously meant to be solved by paper and pencil in a short time frame, why not divide the order total by the price of each item to see if by some chance they ordered multiples of one item?
For example,
15.05/2.15 = 7 mixed fruits
15.05/2.75 = 5.5 french fries.
And then move on to simple combinations...
15 / (2.15 + 2.75) = 3.06122449 mixed fruits with french fries.
In other words, assume that the solution is supposed to be simple and solvable by a human without access to a computer. Then test if the simplest, most obvious (and therefore hidden in plain sight) solution(s) work(s).
I swear I'm pulling this at the local coney this weekend when I order $4.77 worth of appetizers (including tax) at 4:30 AM after the club closes.
