| ( | 912 | − | 3 | x | ) | × | 5 | = | 12 | ( | 600 | − | 4 | x | ) |
| 方程左边 = | 912 | × | 5 | − | 3 | x | × | 5 |
| = | 4560 | − | 15 | x |
| 4560 | − | 15 | x | = | 12 | ( | 600 | − | 4 | x | ) |
| 方程右边 = | 12 | × | 600 | − | 12 | × | 4 | x |
| = | 7200 | − | 48 | x |
| 4560 | − | 15 | x | = | 7200 | − | 48 | x |
| - | 15 | x | + | 48 | x | = | 7200 | − | 4560 |
| 33 | x | = | 7200 | − | 4560 |
| 33 | x | = | 2640 |
| x | = | 2640 | ÷ | 33 |
| = | 2640 | × | 1 33 |
| = | 80 | × | 1 |
| x | = | 80 |