| ( | 4 | + | x | ) | ( | 160 | − | 20 | x | ) | = | 700 |
| Left side of the equation = | 4 | ( | 160 | − | 20 | x | ) | + | x | ( | 160 | − | 20 | x | ) |
| = | 4 | × | 160 | − | 4 | × | 20 | x | + | x | ( | 160 | − | 20 | x | ) |
| = | 640 | − | 80 | x | + | x | ( | 160 | − | 20 | x | ) |
| = | 640 | − | 80 | x | + | x | × | 160 | − | x | × | 20 | x |
| = | 640 | + | 80 | x | − | x | × | 20 | x |
| 640 | + | 80 | x | − | x | × | 20 | x | = | 700 |