| ( | 60 | − | x | − | 45 | ) | ( | 40 | + | 20 | x | ) | = | 1440 |
| Left side of the equation = | 60 | ( | 40 | + | 20 | x | ) | − | x | ( | 40 | + | 20 | x | ) | − | 45 | ( | 40 | + | 20 | x | ) |
| = | 60 | × | 40 | + | 60 | × | 20 | x | − | x | ( | 40 | + | 20 | x | ) | − | 45 | ( | 40 | + | 20 | x | ) |
| = | 2400 | + | 1200 | x | − | x | ( | 40 | + | 20 | x | ) | − | 45 | ( | 40 | + | 20 | x | ) |
| = | 2400 | + | 1200 | x | − | x | × | 40 | − | x | × | 20 | x | − | 45 | ( | 40 | + | 20 | x | ) |
| = | 2400 | + | 1160 | x | − | x | × | 20 | x | − | 45 | ( | 40 | + | 20 | x | ) |
| = | 2400 | + | 1160 | x | − | x | × | 20 | x | − | 45 | × | 40 | − | 45 | × | 20 | x |
| = | 2400 | + | 1160 | x | − | x | × | 20 | x | − | 1800 | − | 900 | x |
| = | 600 | + | 260 | x | − | x | × | 20 | x |
| 600 | + | 260 | x | − | x | × | 20 | x | = | 1440 |