| 420 | + | 16 5 | ( | x | − | 120 | ) | + | 7 2 | ( | 400 | − | x | ) | = | 1336 |
| 方程左边 = | 420 | + | 16 5 | x | − | 16 5 | × | 120 | + | 7 2 | ( | 400 | − | x | ) |
| = | 420 | + | 16 5 | x | − | 384 | + | 7 2 | ( | 400 | − | x | ) |
| = | 36 | + | 16 5 | x | + | 7 2 | ( | 400 | − | x | ) |
| = | 36 | + | 16 5 | x | + | 7 2 | × | 400 | − | 7 2 | x |
| = | 36 | + | 16 5 | x | + | 1400 | − | 7 2 | x |
| = | 1436 | − | 3 10 | x |
| 1436 | − | 3 10 | x | = | 1336 |
| - | 3 10 | x | = | 1336 | − | 1436 |
| - | 3 10 | x | = | - | 100 |
| 100 | = | 3 10 | x |
3 10 | x | = | 100 |
| x | = | 100 | ÷ | 3 10 |
| = | 100 | × | 10 3 |
| x | = | 1000 3 |
| x | = | 333.333333 |