| 20 | x | + | ( | 20 | x | + | 350 | ) | × | 2 | + | 15 | x | = | 100 | x |
| 方程左边 = | 35 | x | + | ( | 20 | x | + | 350 | ) | × | 2 |
| 35 | x | + | ( | 20 | x | + | 350 | ) | × | 2 | = | 100 | x |
| 方程左边 = | 35 | x | + | 20 | x | × | 2 | + | 350 | × | 2 |
| = | 35 | x | + | 40 | x | + | 700 |
| = | 75 | x | + | 700 |
| 75 | x | + | 700 | = | 100 | x |
| 75 | x | − | 100 | x | = | - | 700 |
| - | 25 | x | = | - | 700 |
| 700 | = | 25 | x |
| 25 | x | = | 700 |
| x | = | 700 | ÷ | 25 |
| = | 700 | × | 1 25 |
| = | 28 | × | 1 |
| x | = | 28 |