| ( | x | − | 19 | ) | ( | - | 3 | x | + | 180 | ) | − | ( | - | 3 | x | + | 180 | ) | = | 900 |
| Left side of the equation = | x | ( | - | 3 | x | + | 180 | ) | − | 19 | ( | - | 3 | x | + | 180 | ) | − | ( | - | 3 | x | + | 180 | ) |
| = | - | x | × | 3 | x | + | x | × | 180 | − | 19 | ( | - | 3 | x | + | 180 | ) | − | ( | - | 3 | x | + | 180 | ) |
| = | - | x | × | 3 | x | + | 180 | x | + | 19 | × | 3 | x | − | 19 | × | 180 | − | ( | - | 3 | x | + | 180 | ) |
| = | - | x | × | 3 | x | + | 180 | x | + | 57 | x | − | 3420 | − | ( | - | 3 | x | + | 180 | ) |
| = | - | x | × | 3 | x | + | 237 | x | − | 3420 | − | ( | - | 3 | x | + | 180 | ) |
| = | - | x | × | 3 | x | + | 237 | x | − | 3420 | + | 3 | x | − | 180 |
| = | - | x | × | 3 | x | + | 240 | x | − | 3600 |
| - | x | × | 3 | x | + | 240 | x | − | 3600 | = | 900 |