| ( | 12 | − | y | ) | ( | 100 | + | 20 | y | ) | = | 1500 |
| Left side of the equation = | 12 | ( | 100 | + | 20 | y | ) | − | y | ( | 100 | + | 20 | y | ) |
| = | 12 | × | 100 | + | 12 | × | 20 | y | − | y | ( | 100 | + | 20 | y | ) |
| = | 1200 | + | 240 | y | − | y | ( | 100 | + | 20 | y | ) |
| = | 1200 | + | 240 | y | − | y | × | 100 | − | y | × | 20 | y |
| = | 1200 | + | 140 | y | − | y | × | 20 | y |
| 1200 | + | 140 | y | − | y | × | 20 | y | = | 1500 |