| ( | 90 | × | 3 10 | ) | − | x | = | 1 5 | ( | 90 | − | x | ) |
| Left side of the equation = | 90 | × | 3 10 | − | x |
| = | 27 | − | x |
| 27 | − | x | = | 1 5 | ( | 90 | − | x | ) |
| Right side of the equation = | 1 5 | × | 90 | − | 1 5 | x |
| = | 18 | − | 1 5 | x |
| 27 | − | x | = | 18 | − | 1 5 | x |
| - | x | + | 1 5 | x | = | 18 | − | 27 |
| - | 4 5 | x | = | 18 | − | 27 |
| - | 4 5 | x | = | - | 9 |
| 9 | = | 4 5 | x |
4 5 | x | = | 9 |
| x | = | 9 | ÷ | 4 5 |
| = | 9 | × | 5 4 |
| x | = | 45 4 |
| x | = | 11.25 |