| 90 | ÷ | x | = | 129 | ÷ | x | + | 3 | × | 3 | ÷ | 4 |
| Multiply both sides of the equation by: | x |
| 90 | = | 129 | ÷ | 1 | × | 1 | + | 3 | × | 3 | ÷ | 4 | × | x |
| - | 3 | × | 3 | ÷ | 4 | × | x | = | 129 | ÷ | 1 | × | 1 | − | 90 |
| - | 9 4 | x | = | 129 | ÷ | 1 | × | 1 | − | 90 |
| - | 9 4 | x | = | 129 | − | 90 |
| - | 9 4 | x | = | 39 |
| - | 39 | = | 9 4 | x |
9 4 | x | = | - | 39 |
| x | = | - | 39 | ÷ | 9 4 |
| = | - | 39 | × | 4 9 |
| = | - | 13 | × | 4 3 |
| x | = | - | 52 3 |
| x | = | - 17.333333 |