Can anyone tell me how you find the Chance Cards on Monopoly Sudoku?

THe Chance cards will show as question marks when you first load a puzzle.
 
Once they disappear, there will be a little orange triangle in the upper left corner of the square they are in.
 
Each difficulty level has a different number: Beginner – 1, Easy – 2, Medium – 3, Hard – 4 , and Expert – 5.