| ( | x | − | 40 | ) | ( | 480 | − | 4 | x | ) | = | 14000 |
| Left side of the equation = | x | ( | 480 | − | 4 | x | ) | − | 40 | ( | 480 | − | 4 | x | ) |
| = | x | × | 480 | − | x | × | 4 | x | − | 40 | ( | 480 | − | 4 | x | ) |
| = | 480 | x | − | x | × | 4 | x | − | 40 | × | 480 | + | 40 | × | 4 | x |
| = | 480 | x | − | x | × | 4 | x | − | 19200 | + | 160 | x |
| = | 640 | x | − | x | × | 4 | x | − | 19200 |
| 640 | x | − | x | × | 4 | x | − | 19200 | = | 14000 |