[Haskell-beginners] Help with improving a program

Hi I'm just starting with haskell and want some help with it. I tried to solve the Store Credit[1] problem from google code jam just to practice, the result was a slow code[2] that I find hard to read. Can you guys give me some directions on how to improve it? [1] - https://code.google.com/codejam/contest/351101/dashboard#s=p0 [2] - http://pastebin.com/jNGxGP5H