| 21 | ÷ | 6 | × | x | = | 133 | ÷ | 30 | × | x | − | 120 |
| Left side of the equation = | 7 2 | x |
7 2 | x | = | 133 | ÷ | 30 | × | x | − | 120 |
| Right side of the equation = | 133 30 | x | − | 120 |
7 2 | x | = | 133 30 | x | − | 120 |
7 2 | x | − | 133 30 | x | = | - | 120 |
| - | 14 15 | x | = | - | 120 |
| 120 | = | 14 15 | x |
14 15 | x | = | 120 |
| x | = | 120 | ÷ | 14 15 |
| = | 120 | × | 15 14 |
| = | 60 | × | 15 7 |
| x | = | 900 7 |
| x | = | 128.571429 |