| ( | 40 | − | x | − | 30 | ) | ( | 200 | x | + | 600 | ) | = | 8400 |
| Left side of the equation = | 40 | ( | 200 | x | + | 600 | ) | − | x | ( | 200 | x | + | 600 | ) | − | 30 | ( | 200 | x | + | 600 | ) |
| = | 40 | × | 200 | x | + | 40 | × | 600 | − | x | ( | 200 | x | + | 600 | ) | − | 30 | ( | 200 | x | + | 600 | ) |
| = | 8000 | x | + | 24000 | − | x | ( | 200 | x | + | 600 | ) | − | 30 | ( | 200 | x | + | 600 | ) |
| = | 8000 | x | + | 24000 | − | x | × | 200 | x | − | x | × | 600 | − | 30 | ( | 200 | x | + | 600 | ) |
| = | 7400 | x | + | 24000 | − | x | × | 200 | x | − | 30 | ( | 200 | x | + | 600 | ) |
| = | 7400 | x | + | 24000 | − | x | × | 200 | x | − | 30 | × | 200 | x | − | 30 | × | 600 |
| = | 7400 | x | + | 24000 | − | x | × | 200 | x | − | 6000 | x | − | 18000 |
| = | 1400 | x | + | 6000 | − | x | × | 200 | x |
| 1400 | x | + | 6000 | − | x | × | 200 | x | = | 8400 |