| ( | 18 | − | 12 | ) | x | + | ( | 6 | − | 4 | ) | ( | 20 | − | x | ) | = | 300 |
| 方程左边 = | 18 | x | − | 12 | x | + | ( | 6 | − | 4 | ) | ( | 20 | − | x | ) |
| = | 6 | x | + | ( | 6 | − | 4 | ) | ( | 20 | − | x | ) |
| = | 6 | x | + | 6 | ( | 20 | − | x | ) | − | 4 | ( | 20 | − | x | ) |
| = | 6 | x | + | 6 | × | 20 | − | 6 | x | − | 4 | ( | 20 | − | x | ) |
| = | 6 | x | + | 120 | − | 6 | x | − | 4 | ( | 20 | − | x | ) |
| = | 0 | x | + | 120 | − | 4 | ( | 20 | − | x | ) |
| = | 120 | − | 4 | × | 20 | + | 4 | x |
| = | 120 | − | 80 | + | 4 | x |
| = | 40 | + | 4 | x |
| 40 | + | 4 | x | = | 300 |
| 4 | x | = | 300 | − | 40 |
| 4 | x | = | 260 |
| x | = | 260 | ÷ | 4 |
| = | 260 | × | 1 4 |
| = | 65 | × | 1 |
| x | = | 65 |