| 35 | × | 40 | + | ( | 225 | − | a% | × | 225 | − | 150 | ) | × | 20 | = | 2000 |
| 方程左边 = | 1400 | + | ( | 225 | − | a% | × | 225 | − | 150 | ) | × | 20 |
| 1400 | + | ( | 225 | − | a% | × | 225 | − | 150 | ) | × | 20 | = | 2000 |
| 方程左边 = | 1400 | + | 225 | × | 20 | − | a% | × | 225 | × | 20 | − | 150 | × | 20 |
| = | 1400 | + | 4500 | − | 45 | a | − | 3000 |
| = | 2900 | − | 45 | a |
| 2900 | − | 45 | a | = | 2000 |
| - | 45 | a | = | 2000 | − | 2900 |
| - | 45 | a | = | - | 900 |
| 900 | = | 45 | a |
| 45 | a | = | 900 |
| a | = | 900 | ÷ | 45 |
| = | 900 | × | 1 45 |
| = | 20 | × | 1 |
| a | = | 20 |