| ( | 80 | + | x | ) | ( | 53 | − | x | ) | = | 51 | × | 80 |
| Left side of the equation = | 80 | ( | 53 | − | x | ) | + | x | ( | 53 | − | x | ) |
| = | 80 | × | 53 | − | 80 | x | + | x | ( | 53 | − | x | ) |
| = | 4240 | − | 80 | x | + | x | ( | 53 | − | x | ) |
| = | 4240 | − | 80 | x | + | x | × | 53 | − | x | x |
| = | 4240 | − | 27 | x | − | x | x |
| 4240 | − | 27 | x | − | x | x | = | 51 | × | 80 |
| Right side of the equation = | 4080 |
| 4240 | − | 27 | x | − | x | x | = | 4080 |