| 5 | ÷ | 7 | × | ( | 3 | x | − | 20 | ) | = | x | + | 20 |
| 方程左边 = | 5 7 | ( | 3 | x | − | 20 | ) |
5 7 | ( | 3 | x | − | 20 | ) | = | x | + | 20 |
| 方程左边 = | 5 7 | × | 3 | x | − | 5 7 | × | 20 |
| = | 15 7 | x | − | 100 7 |
15 7 | x | − | 100 7 | = | x | + | 20 |
15 7 | x | − | x | = | 20 | + | 100 7 |
8 7 | x | = | 20 | + | 100 7 |
8 7 | x | = | 240 7 |
| x | = | 240 7 | ÷ | 8 7 |
| = | 240 7 | × | 7 8 |
| = | 30 | × | 1 |
| x | = | 30 |