| ( | 30 | + | x | ) | ( | 230 | − | 10 | x | ) | = | 252 |
| Left side of the equation = | 30 | ( | 230 | − | 10 | x | ) | + | x | ( | 230 | − | 10 | x | ) |
| = | 30 | × | 230 | − | 30 | × | 10 | x | + | x | ( | 230 | − | 10 | x | ) |
| = | 6900 | − | 300 | x | + | x | ( | 230 | − | 10 | x | ) |
| = | 6900 | − | 300 | x | + | x | × | 230 | − | x | × | 10 | x |
| = | 6900 | − | 70 | x | − | x | × | 10 | x |
| 6900 | − | 70 | x | − | x | × | 10 | x | = | 252 |