| ( | 100 | − | a | ) | ÷ | ( | a | − | 88 | ) | = | 15 |
| Multiply both sides of the equation by: | ( | a | − | 88 | ) |
| ( | 100 | − | a | ) | = | 15 | ( | a | − | 88 | ) |
| 100 | − | a | = | 15 | ( | a | − | 88 | ) |
| 100 | − | a | = | 15 | a | − | 15 | × | 88 |
| 100 | − | a | = | 15 | a | − | 1320 |
| - | a | − | 15 | a | = | - | 1320 | − | 100 |
| - | 16 | a | = | - | 1320 | − | 100 |
| - | 16 | a | = | - | 1420 |
| 1420 | = | 16 | a |
| 16 | a | = | 1420 |
| a | = | 1420 | ÷ | 16 |
| = | 1420 | × | 1 16 |
| = | 355 | × | 1 4 |
| a | = | 355 4 |
| a | = | 88.75 |