| ( | 169 | + | X | ) | ÷ | ( | 207 | + | X | ) | = | 9 10 |
| Multiply both sides of the equation by: | ( | 207 | + | X | ) |
| ( | 169 | + | X | ) | = | 9 10 | ( | 207 | + | X | ) |
| 169 | + | X | = | 9 10 | ( | 207 | + | X | ) |
| 169 | + | X | = | 9 10 | × | 207 | + | 9 10 | X |
| 169 | + | X | = | 1863 10 | + | 9 10 | X |
| X | − | 9 10 | X | = | 1863 10 | − | 169 |
1 10 | X | = | 1863 10 | − | 169 |
1 10 | X | = | 173 10 |
| X | = | 173 10 | ÷ | 1 10 |
| = | 173 10 | × | 10 |
| = | 173 | × | 1 |
| X | = | 173 |