PDF WASTEWATER OPERATOR EXAMINATION STUDY KEY CLASS III AND CLASS ... - Indiana There are a few basic rules that apply to solving formulas: 1. Work from left to right 2. Do all of the multiplication and division above the line (in the numerator) and below the line (in the denominator); then do the addition and subtraction above and below the line. 3. Perform the division (divide the numerator by the denominator). 4.