| 3 | x | × | 300 | + | 500 | x | + | ( | 100 | − | 4 | x | ) | × | 600 | = | 45000 |
| Left side of the equation = | 900 | x | + | 500 | x | + | ( | 100 | − | 4 | x | ) | × | 600 |
| = | 1400 | x | + | ( | 100 | − | 4 | x | ) | × | 600 |
| 1400 | x | + | ( | 100 | − | 4 | x | ) | × | 600 | = | 45000 |
| Left side of the equation = | 1400 | x | + | 100 | × | 600 | − | 4 | x | × | 600 |
| = | 1400 | x | + | 60000 | − | 2400 | x |
| = | - | 1000 | x | + | 60000 |
| - | 1000 | x | + | 60000 | = | 45000 |
| - | 1000 | x | = | 45000 | − | 60000 |
| - | 1000 | x | = | - | 15000 |
| 15000 | = | 1000 | x |
| 1000 | x | = | 15000 |
| x | = | 15000 | ÷ | 1000 |
| = | 15000 | × | 1 1000 |
| = | 15 | × | 1 |
| x | = | 15 |