| ( | 120 | × | 400 | + | 100 | ( | 120 | − | x | ) | − | 80 | × | 500 | ) | ÷ | ( | 80 | × | 500 | ) | = | 45 100 |
| Multiply both sides of the equation by: | ( | 80 | × | 500 | ) |
| ( | 120 | × | 400 | + | 100 | ( | 120 | − | x | ) | − | 80 | × | 500 | ) | = | 45 100 | ( | 80 | × | 500 | ) |
| 120 | × | 400 | + | 100 | ( | 120 | − | x | ) | − | 80 | × | 500 | = | 45 100 | ( | 80 | × | 500 | ) |
| 120 | × | 400 | + | 100 | ( | 120 | − | x | ) | − | 80 | × | 500 | = | 45 100 | × | 80 | × | 500 |
| 48000 | + | 100 | ( | 120 | − | x | ) | − | 40000 | = | 18000 |
| 8000 | + | 100 | ( | 120 | − | x | ) | = | 18000 |
| 8000 | + | 100 | × | 120 | − | 100 | x | = | 18000 |
| 8000 | + | 12000 | − | 100 | x | = | 18000 |
| 20000 | − | 100 | x | = | 18000 |
| - | 100 | x | = | 18000 | − | 20000 |
| - | 100 | x | = | - | 2000 |
| 2000 | = | 100 | x |
| 100 | x | = | 2000 |
| x | = | 2000 | ÷ | 100 |
| = | 2000 | × | 1 100 |
| = | 20 | × | 1 |
| x | = | 20 |