| x | ( | 150 | − | 60 | ) | + | 210 | ( | 10 | − | x | ) | = | 1500 |
| 方程左边 = | x | × | 150 | − | x | × | 60 | + | 210 | ( | 10 | − | x | ) |
| = | 90 | x | + | 210 | ( | 10 | − | x | ) |
| = | 90 | x | + | 210 | × | 10 | − | 210 | x |
| = | 90 | x | + | 2100 | − | 210 | x |
| = | - | 120 | x | + | 2100 |
| - | 120 | x | + | 2100 | = | 1500 |
| - | 120 | x | = | 1500 | − | 2100 |
| - | 120 | x | = | - | 600 |
| 600 | = | 120 | x |
| 120 | x | = | 600 |
| x | = | 600 | ÷ | 120 |
| = | 600 | × | 1 120 |
| = | 5 | × | 1 |
| x | = | 5 |