| 3 | ( | 3 | y | − | 1 | ) | − | 12 | = | 2 | ( | 5 | y | − | 7 | ) |
| Left side of the equation = | 3 | × | 3 | y | − | 3 | × | 1 | − | 12 |
| = | 9 | y | − | 3 | − | 12 |
| = | 9 | y | − | 15 |
| 9 | y | − | 15 | = | 2 | ( | 5 | y | − | 7 | ) |
| Right side of the equation = | 2 | × | 5 | y | − | 2 | × | 7 |
| = | 10 | y | − | 14 |
| 9 | y | − | 15 | = | 10 | y | − | 14 |
| 9 | y | − | 10 | y | = | - | 14 | + | 15 |
| - | y | = | - | 14 | + | 15 |
| - | y | = | - | 14 | + | 15 |
| - | y | = | 1 |
| - | 1 | = | y |
| y | = | - | 1 |