| 3000 | ÷ | x | − | 15 | = | 3000 | ÷ | ( | 5 4 | x | ) |
| 方程两边同时乘以: | x | , | ( | 5 4 | × | 1 | ) |
| 3000 | ( | 5 4 | × | 1 | ) | − | 15 | x | ( | 5 4 | × | 1 | ) | = | 3000 | × | 1 |
| 3000 | × | 5 4 | × | 1 | − | 15 | x | ( | 5 4 | × | 1 | ) | = | 3000 | × | 1 |
| 3750 | − | 15 | x | ( | 5 4 | × | 1 | ) | = | 3000 |
| 3750 | − | 15 | x | × | 5 4 | × | 1 | = | 3000 |
| 3750 | − | 75 4 | x | = | 3000 |
| - | 75 4 | x | = | 3000 | − | 3750 |
| - | 75 4 | x | = | - | 750 |
| 750 | = | 75 4 | x |
75 4 | x | = | 750 |
| x | = | 750 | ÷ | 75 4 |
| = | 750 | × | 4 75 |
| = | 10 | × | 4 |
| x | = | 40 |