| ( | 15 | − | y | ) | ( | 100 | + | 5 | y | ) | = | 1250 |
| Left side of the equation = | 15 | ( | 100 | + | 5 | y | ) | − | y | ( | 100 | + | 5 | y | ) |
| = | 15 | × | 100 | + | 15 | × | 5 | y | − | y | ( | 100 | + | 5 | y | ) |
| = | 1500 | + | 75 | y | − | y | ( | 100 | + | 5 | y | ) |
| = | 1500 | + | 75 | y | − | y | × | 100 | − | y | × | 5 | y |
| = | 1500 | − | 25 | y | − | y | × | 5 | y |
| 1500 | − | 25 | y | − | y | × | 5 | y | = | 1250 |