| 1800 | = | 18000 | ÷ | ( | 150 | − | a | ) |
| Multiply both sides of the equation by: | ( | 150 | − | a | ) |
| 1800 | ( | 150 | − | a | ) | = | 18000 |
| 1800 | × | 150 | − | 1800 | a | = | 18000 |
| 270000 | − | 1800 | a | = | 18000 |
| - | 1800 | a | = | 18000 | − | 270000 |
| - | 1800 | a | = | - | 252000 |
| 252000 | = | 1800 | a |
| 1800 | a | = | 252000 |
| a | = | 252000 | ÷ | 1800 |
| = | 252000 | × | 1 1800 |
| = | 140 | × | 1 |
| a | = | 140 |