| 3 | ( | x | − | 50 | ) | + | 6 | ( | x | + | x | − | 50 | ) | = | 2100 |
| 方程左边 = | 3 | x | − | 3 | × | 50 | + | 6 | ( | x | + | x | − | 50 | ) |
| = | 3 | x | − | 150 | + | 6 | ( | x | + | x | − | 50 | ) |
| = | 3 | x | − | 150 | + | 6 | x | + | 6 | x | − | 6 | × | 50 |
| = | 3 | x | − | 150 | + | 6 | x | + | 6 | x | − | 300 |
| = | 15 | x | − | 450 |
| 15 | x | − | 450 | = | 2100 |
| 15 | x | = | 2100 | + | 450 |
| 15 | x | = | 2550 |
| x | = | 2550 | ÷ | 15 |
| = | 2550 | × | 1 15 |
| = | 170 | × | 1 |
| x | = | 170 |