| ( | 900 | × | 200 | ) | + | ( | 90 | − | x | ) | ( | 200 | − | 5 | x | ) | = | 12250 |
| Left side of the equation = | 900 | × | 200 | + | ( | 90 | − | x | ) | ( | 200 | − | 5 | x | ) |
| = | 180000 | + | ( | 90 | − | x | ) | ( | 200 | − | 5 | x | ) |
| = | 180000 | + | 90 | ( | 200 | − | 5 | x | ) | − | x | ( | 200 | − | 5 | x | ) |
| = | 180000 | + | 90 | × | 200 | − | 90 | × | 5 | x | − | x | ( | 200 | − | 5 | x | ) |
| = | 180000 | + | 18000 | − | 450 | x | − | x | ( | 200 | − | 5 | x | ) |
| = | 198000 | − | 450 | x | − | x | ( | 200 | − | 5 | x | ) |
| = | 198000 | − | 450 | x | − | x | × | 200 | + | x | × | 5 | x |
| = | 198000 | − | 650 | x | + | x | × | 5 | x |
| 198000 | − | 650 | x | + | x | × | 5 | x | = | 12250 |