| ( | 280 | × | 80 100 | − | x | ) | ÷ | x | × | 100 100 | = | 12 100 |
| Multiply both sides of the equation by: | x |
| ( | 280 | × | 80 100 | − | x | ) | × | 100 100 | = | 12 100 | x |
| 280 | × | 80 100 | × | 100 100 | − | x | × | 100 100 | = | 12 100 | x |
| 224 | − | x | × | 100 100 | = | 12 100 | x |
| - | 100 100 | x | − | 12 100 | x | = | - | 224 |
| - | 28 25 | x | = | - | 224 |
| 224 | = | 28 25 | x |
28 25 | x | = | 224 |
| x | = | 224 | ÷ | 28 25 |
| = | 224 | × | 25 28 |
| = | 8 | × | 25 |
| x | = | 200 |