Is it true that in this equation:

To make the fraction a whole number (x being a multiple of 99) it is not possible to make the (a-b) and (a+b) make a multiple of 99, with a and b being single digit numbers only.

I don't think so myself. The only possible situation would be used two digit numbers e.g. a as 10 and b as 1. However this would defy the question.