| ( | 25 | − | 7 | ) | × | 4 | + | ( | 25 | − | x | ) | × | 3 | = | 120 |
| Left side of the equation = | 25 | × | 4 | − | 7 | × | 4 | + | ( | 25 | − | x | ) | × | 3 |
| = | 100 | − | 28 | + | ( | 25 | − | x | ) | × | 3 |
| = | 72 | + | ( | 25 | − | x | ) | × | 3 |
| = | 72 | + | 25 | × | 3 | − | x | × | 3 |
| = | 72 | + | 75 | − | x | × | 3 |
| = | 147 | − | 3 | x |
| 147 | − | 3 | x | = | 120 |
| - | 3 | x | = | 120 | − | 147 |
| - | 3 | x | = | - | 27 |
| 27 | = | 3 | x |
| 3 | x | = | 27 |
| x | = | 27 | ÷ | 3 |
| = | 27 | × | 1 3 |
| = | 9 | × | 1 |
| x | = | 9 |