| 40 | × | 45 | + | ( | x | − | 40 | ) | × | 15 | = | ( | 40 | × | 15 | + | 15 | x | ) | ÷ | 100 | × | 80 |
| Left side of the equation = | 1800 | + | ( | x | − | 40 | ) | × | 15 |
| 1800 | + | ( | x | − | 40 | ) | × | 15 | = | ( | 40 | × | 15 | + | 15 | x | ) | ÷ | 100 | × | 80 |
| Left side of the equation = | 1800 | + | x | × | 15 | − | 40 | × | 15 |
| = | 1800 | + | x | × | 15 | − | 600 |
| = | 1200 | + | 15 | x |
| 1200 | + | 15 | x | = | ( | 40 | × | 15 | + | 15 | x | ) | ÷ | 100 | × | 80 |
| Right side of the equation = | ( | 40 | × | 15 | + | 15 | x | ) | × | 4 5 |
| 1200 | + | 15 | x | = | ( | 40 | × | 15 | + | 15 | x | ) | × | 4 5 |
| Right side of the equation = | 40 | × | 15 | × | 4 5 | + | 15 | x | × | 4 5 |
| = | 480 | + | 12 | x |
| 1200 | + | 15 | x | = | 480 | + | 12 | x |
| 15 | x | − | 12 | x | = | 480 | − | 1200 |
| 3 | x | = | 480 | − | 1200 |
| 3 | x | = | - | 720 |
| x | = | - | 720 | ÷ | 3 |
| = | - | 720 | × | 1 3 |
| = | - | 240 | × | 1 |
| x | = | - | 240 |