| ( | x | − | 30 | ) | ( | 3 | x | − | 60 | ) | = | 1800 |
| Left side of the equation = | x | ( | 3 | x | − | 60 | ) | − | 30 | ( | 3 | x | − | 60 | ) |
| = | x | × | 3 | x | − | x | × | 60 | − | 30 | ( | 3 | x | − | 60 | ) |
| = | x | × | 3 | x | − | 60 | x | − | 30 | × | 3 | x | + | 30 | × | 60 |
| = | x | × | 3 | x | − | 60 | x | − | 90 | x | + | 1800 |
| = | x | × | 3 | x | − | 150 | x | + | 1800 |
| x | × | 3 | x | − | 150 | x | + | 1800 | = | 1800 |