| ( | 1200 | + | 100 | ( | x | + | 3 | ) | ) | × | 2 | − | 600 | x | = | 0 |
| 方程左边 = | 1200 | × | 2 | + | 100 | ( | x | + | 3 | ) | × | 2 | − | 600 | x |
| = | 2400 | + | 200 | ( | x | + | 3 | ) | − | 600 | x |
| = | 2400 | + | 200 | x | + | 200 | × | 3 | − | 600 | x |
| = | 2400 | + | 200 | x | + | 600 | − | 600 | x |
| = | 3000 | − | 400 | x |
| 3000 | − | 400 | x | = | 0 |
| - | 400 | x | = | 0 | − | 3000 |
| - | 400 | x | = | - | 3000 |
| 3000 | = | 400 | x |
| 400 | x | = | 3000 |
| x | = | 3000 | ÷ | 400 |
| = | 3000 | × | 1 400 |
| = | 15 | × | 1 2 |
| x | = | 15 2 |
| x | = | 7.5 |