| ( | 90 | − | x | ) | ( | 1 | − | 60 100 | − | 8 500 | x | ) | = | 12 |
| Left side of the equation = | 90 | ( | 1 | − | 60 100 | − | 8 500 | x | ) | − | x | ( | 1 | − | 60 100 | − | 8 500 | x | ) |
| = | 90 | × | 1 | − | 90 | × | 60 100 | − | 90 | × | 8 500 | x | − | x | ( | 1 | − | 60 100 | − | 8 500 | x | ) |
| = | 90 | − | 54 | − | 36 25 | x | − | x | ( | 1 | − | 60 100 | − | 8 500 | x | ) |
| = | 36 | − | 36 25 | x | − | x | ( | 1 | − | 60 100 | − | 8 500 | x | ) |
| = | 36 | − | 36 25 | x | − | x | × | 1 | + | x | × | 60 100 | + | x | × | 8 500 | x |
| = | 36 | − | 46 25 | x | + | x | × | 8 500 | x |
| 36 | − | 46 25 | x | + | x | × | 8 500 | x | = | 12 |