| ( | ( | 7 | − | x | ) | × | 6 | + | 20 | ) | x | + | 7 | ( | 40 | − | x | ) | = | 340 |
| Left side of the equation = | ( | 7 | − | x | ) | × | 6 | x | + | 20 | x | + | 7 | ( | 40 | − | x | ) |
| = | 7 | × | 6 | x | − | x | × | 6 | x | + | 20 | x | + | 7 | ( | 40 | − | x | ) |
| = | 42 | x | − | x | × | 6 | x | + | 20 | x | + | 7 | ( | 40 | − | x | ) |
| = | 62 | x | − | x | × | 6 | x | + | 7 | ( | 40 | − | x | ) |
| = | 62 | x | − | x | × | 6 | x | + | 7 | × | 40 | − | 7 | x |
| = | 62 | x | − | x | × | 6 | x | + | 280 | − | 7 | x |
| = | 55 | x | − | x | × | 6 | x | + | 280 |
| 55 | x | − | x | × | 6 | x | + | 280 | = | 340 |