| ( | 11 | + | 3 | ) | x | + | ( | 15 | + | 5 | ) | ( | 800 | − | x | ) | = | 13900 |
| 方程左边 = | 11 | x | + | 3 | x | + | ( | 15 | + | 5 | ) | ( | 800 | − | x | ) |
| = | 14 | x | + | ( | 15 | + | 5 | ) | ( | 800 | − | x | ) |
| = | 14 | x | + | 15 | ( | 800 | − | x | ) | + | 5 | ( | 800 | − | x | ) |
| = | 14 | x | + | 15 | × | 800 | − | 15 | x | + | 5 | ( | 800 | − | x | ) |
| = | 14 | x | + | 12000 | − | 15 | x | + | 5 | ( | 800 | − | x | ) |
| = | - | 1 | x | + | 12000 | + | 5 | ( | 800 | − | x | ) |
| = | - | 1 | x | + | 12000 | + | 5 | × | 800 | − | 5 | x |
| = | - | 1 | x | + | 12000 | + | 4000 | − | 5 | x |
| = | - | 6 | x | + | 16000 |
| - | 6 | x | + | 16000 | = | 13900 |
| - | 6 | x | = | 13900 | − | 16000 |
| - | 6 | x | = | - | 2100 |
| 2100 | = | 6 | x |
| 6 | x | = | 2100 |
| x | = | 2100 | ÷ | 6 |
| = | 2100 | × | 1 6 |
| = | 350 | × | 1 |
| x | = | 350 |