| 200 | × | 150 | + | 300 | ( | 1200 | x | − | 1000 | ) | = | 18000 |
| 方程左边 = | 30000 | + | 300 | ( | 1200 | x | − | 1000 | ) |
| 30000 | + | 300 | ( | 1200 | x | − | 1000 | ) | = | 18000 |
| 方程左边 = | 30000 | + | 300 | × | 1200 | x | − | 300 | × | 1000 |
| = | 30000 | + | 360000 | x | − | 300000 |
| = | - | 270000 | + | 360000 | x |
| - | 270000 | + | 360000 | x | = | 18000 |
| 360000 | x | = | 18000 | + | 270000 |
| 360000 | x | = | 288000 |
| x | = | 288000 | ÷ | 360000 |
| = | 288000 | × | 1 360000 |
| = | 4 | × | 1 5 |
| x | = | 4 5 |
| x | = | 0.8 |