6 5 | ( | 420 | − | y | ) | + | 72 | = | 6 5 | y | − | 72 |
| Left side of the equation = | 6 5 | × | 420 | − | 6 5 | y | + | 72 |
| = | 504 | − | 6 5 | y | + | 72 |
| = | 576 | − | 6 5 | y |
| 576 | − | 6 5 | y | = | 6 5 | y | − | 72 |
| - | 6 5 | y | − | 6 5 | y | = | - | 72 | − | 576 |
| - | 12 5 | y | = | - | 72 | − | 576 |
| - | 12 5 | y | = | - | 648 |
| 648 | = | 12 5 | y |
12 5 | y | = | 648 |
| y | = | 648 | ÷ | 12 5 |
| = | 648 | × | 5 12 |
| = | 54 | × | 5 |
| y | = | 270 |