| ( | 300 | + | X | ) | ÷ | ( | 1000 | + | X | ) | = | 99 100 |
| Multiply both sides of the equation by: | ( | 1000 | + | X | ) |
| ( | 300 | + | X | ) | = | 99 100 | ( | 1000 | + | X | ) |
| 300 | + | X | = | 99 100 | ( | 1000 | + | X | ) |
| 300 | + | X | = | 99 100 | × | 1000 | + | 99 100 | X |
| 300 | + | X | = | 990 | + | 99 100 | X |
| X | − | 99 100 | X | = | 990 | − | 300 |
1 100 | X | = | 990 | − | 300 |
1 100 | X | = | 690 |
| X | = | 690 | ÷ | 1 100 |
| = | 690 | × | 100 |
| X | = | 69000 |