| 900 | ÷ | x | = | 1200 | ÷ | ( | x | + | 20 | ) |
| Multiply both sides of the equation by: | x | , | ( | x | + | 20 | ) |
| 900 | ( | x | + | 20 | ) | = | 1200 | x |
| 900 | x | + | 900 | × | 20 | = | 1200 | x |
| 900 | x | + | 18000 | = | 1200 | x |
| 900 | x | − | 1200 | x | = | - | 18000 |
| - | 300 | x | = | - | 18000 |
| 18000 | = | 300 | x |
| 300 | x | = | 18000 |
| x | = | 18000 | ÷ | 300 |
| = | 18000 | × | 1 300 |
| = | 60 | × | 1 |
| x | = | 60 |