| x | ( | 5 | ( | 60 | − | x | ) | + | 400 | ) | − | 40 | ( | 5 | ( | 60 | − | x | ) | + | 400 | ) | = | 10500 |
| Left side of the equation = | x | × | 5 | ( | 60 | − | x | ) | + | x | × | 400 | − | 40 | ( | 5 | ( | 60 | − | x | ) | + | 400 | ) |
| = | x | × | 5 | × | 60 | − | x | × | 5 | x | + | 400 | x | − | 40 | ( | 5 | ( | 60 | − | x | ) | + | 400 | ) |
| = | x | × | 300 | − | x | × | 5 | x | + | 400 | x | − | 40 | ( | 5 | ( | 60 | − | x | ) | + | 400 | ) |
| = | 700 | x | − | x | × | 5 | x | − | 40 | ( | 5 | ( | 60 | − | x | ) | + | 400 | ) |
| = | 700 | x | − | x | × | 5 | x | − | 40 | × | 5 | ( | 60 | − | x | ) | − | 40 | × | 400 |
| = | 700 | x | − | x | × | 5 | x | − | 200 | ( | 60 | − | x | ) | − | 16000 |
| = | 700 | x | − | x | × | 5 | x | − | 200 | × | 60 | + | 200 | x | − | 16000 |
| = | 700 | x | − | x | × | 5 | x | − | 12000 | + | 200 | x | − | 16000 |
| = | 900 | x | − | x | × | 5 | x | − | 28000 |
| 900 | x | − | x | × | 5 | x | − | 28000 | = | 10500 |