Each time your user total changes, I would have it trigger a check to see if it's correct.
If it is, set an offscreen object to "selected". If it's incorrect, set the offscreen object to "normal".
e.g. if vChange is a variable containing the current amount of change and cChange is a constant programmed with the required amount:
When vChange changes, if vChange = variable cChange change state of Answer to Selected, else change state of Answer to normal
Set your quiz as multiple choice and have the correct answer be the offscreen object "Answer". So when you submit, it's only checking to see if the offscreen object has been selected.
