Help with interaction on slide

The challenge with this is knowing when the number selected is the first, second and third.

I'd probably have three layers for each number with a tracking number variable:

• hundred
  • varHundred = [1 = 100]
  • show layer ten when varHundred changes 
• ten
  • varTen = [1 = 10]
  • show layer one when varTen changes 
  •  
• one
  • varOne = [1 = 1]
• Add the variables together
  • TotalVar
  • Add VarH to Var
• Assuming they need to enter # at the end, this could be the submit button that does the adding. Otherwise, the submit button could add the variables. You should end up with a value up to 999 and the # sign. You can evaluate that to display correct/incorrect.

Side note: since you're using a phone image, I'd probably not use a submit button since phones don't have a submit. Perhaps the # is the submit.