| ( | 90 | − | 60 | − | 5 | ) | x | + | ( | 140 | − | 100 | − | 10 | ) | ( | 100 | − | x | ) | = | 0 |
| Left side of the equation = | 90 | x | − | 60 | x | − | 5 | x | + | ( | 140 | − | 100 | − | 10 | ) | ( | 100 | − | x | ) |
| = | 25 | x | + | ( | 140 | − | 100 | − | 10 | ) | ( | 100 | − | x | ) |
| = | 25 | x | + | 140 | ( | 100 | − | x | ) | − | 100 | ( | 100 | − | x | ) | − | 10 | ( | 100 | − | x | ) |
| = | 25 | x | + | 140 | × | 100 | − | 140 | x | − | 100 | ( | 100 | − | x | ) | − | 10 | ( | 100 | − | x | ) |
| = | 25 | x | + | 14000 | − | 140 | x | − | 100 | ( | 100 | − | x | ) | − | 10 | ( | 100 | − | x | ) |
| = | - | 115 | x | + | 14000 | − | 100 | ( | 100 | − | x | ) | − | 10 | ( | 100 | − | x | ) |
| = | - | 115 | x | + | 14000 | − | 100 | × | 100 | + | 100 | x | − | 10 | ( | 100 | − | x | ) |
| = | - | 115 | x | + | 14000 | − | 10000 | + | 100 | x | − | 10 | ( | 100 | − | x | ) |
| = | - | 15 | x | + | 4000 | − | 10 | ( | 100 | − | x | ) |
| = | - | 15 | x | + | 4000 | − | 10 | × | 100 | + | 10 | x |
| = | - | 15 | x | + | 4000 | − | 1000 | + | 10 | x |
| = | - | 5 | x | + | 3000 |
| - | 5 | x | + | 3000 | = | 0 |
| - | 5 | x | = | 0 | − | 3000 |
| - | 5 | x | = | - | 3000 |
| 3000 | = | 5 | x |
| 5 | x | = | 3000 |
| x | = | 3000 | ÷ | 5 |
| = | 3000 | × | 1 5 |
| = | 600 | × | 1 |
| x | = | 600 |