| ( | 33 | + | x | ) | ÷ | ( | 40 | + | x | ) | = | 90 100 |
| Multiply both sides of the equation by: | ( | 40 | + | x | ) |
| ( | 33 | + | x | ) | = | 90 100 | ( | 40 | + | x | ) |
| 33 | + | x | = | 90 100 | ( | 40 | + | x | ) |
| 33 | + | x | = | 90 100 | × | 40 | + | 90 100 | x |
| 33 | + | x | = | 36 | + | 90 100 | x |
| x | − | 90 100 | x | = | 36 | − | 33 |
1 10 | x | = | 36 | − | 33 |
1 10 | x | = | 3 |
| x | = | 3 | ÷ | 1 10 |
| = | 3 | × | 10 |
| x | = | 30 |