| ( | 600 | + | x | ) | ÷ | ( | 140 | + | x | ) | = | 3 |
| 方程两边同时乘以: | ( | 140 | + | x | ) |
| ( | 600 | + | x | ) | = | 3 | ( | 140 | + | x | ) |
| 600 | + | x | = | 3 | ( | 140 | + | x | ) |
| 600 | + | x | = | 3 | × | 140 | + | 3 | x |
| 600 | + | x | = | 420 | + | 3 | x |
| x | − | 3 | x | = | 420 | − | 600 |
| - | 2 | x | = | 420 | − | 600 |
| - | 2 | x | = | - | 180 |
| 180 | = | 2 | x |
| 2 | x | = | 180 |
| x | = | 180 | ÷ | 2 |
| = | 180 | × | 1 2 |
| = | 90 | × | 1 |
| x | = | 90 |