| 200 | x | + | 200 | × | 2 | x | + | ( | 500 | − | 3 | x | ) | × | 300 | = | 120000 |
| Left side of the equation = | 200 | x | + | 400 | x | + | ( | 500 | − | 3 | x | ) | × | 300 |
| = | 600 | x | + | ( | 500 | − | 3 | x | ) | × | 300 |
| 600 | x | + | ( | 500 | − | 3 | x | ) | × | 300 | = | 120000 |
| Left side of the equation = | 600 | x | + | 500 | × | 300 | − | 3 | x | × | 300 |
| = | 600 | x | + | 150000 | − | 900 | x |
| = | - | 300 | x | + | 150000 |
| - | 300 | x | + | 150000 | = | 120000 |
| - | 300 | x | = | 120000 | − | 150000 |
| - | 300 | x | = | - | 30000 |
| 30000 | = | 300 | x |
| 300 | x | = | 30000 |
| x | = | 30000 | ÷ | 300 |
| = | 30000 | × | 1 300 |
| = | 100 | × | 1 |
| x | = | 100 |