| ( | 80 | + | 70 | ) | ÷ | ( | 90 100 | − | 75 100 | ) | = | x |
| Multiply both sides of the equation by: | ( | 90 100 | − | 75 100 | ) |
| ( | 80 | + | 70 | ) | = | x | ( | 90 100 | − | 75 100 | ) |
| 80 | + | 70 | = | x | ( | 90 100 | − | 75 100 | ) |
| 80 | + | 70 | = | x | × | 90 100 | − | x | × | 75 100 |
| 150 | = | 3 20 | x |
| - | 3 20 | x | = | - | 150 |
| 150 | = | 3 20 | x |
3 20 | x | = | 150 |
| x | = | 150 | ÷ | 3 20 |
| = | 150 | × | 20 3 |
| = | 50 | × | 20 |
| x | = | 1000 |