[Haskell-cafe] need help on exercise

Hi, I am working on exercise 12.5 from "Haskell, The Craft of Functional Programming, second edition" by Simon Thompson. It asks to make Int an instance in the Visible class. I have tried multiple ways of doing this however I keep receiving the same error messege when I compile my program, saying that my types do not match and i have given a (Num a, Visible a) => String, when it is supposed to be an Int -> String. If anyone could help me with this issue it would be greatly appreciated. Thanks, Kelly