| 3 | ( | 60 | + | x | × | 3 | ÷ | 2 | ) | ( | 40 | + | x | ) | = | 642 |
| 方程左边 = | 3 | × | 60 | ( | 40 | + | x | ) | + | 3 | x | × | 3 | ÷ | 2 | × | ( | 40 | + | x | ) |
| = | 180 | ( | 40 | + | x | ) | + | 9 2 | x | ( | 40 | + | x | ) |
| = | 180 | × | 40 | + | 180 | x | + | 9 2 | x | ( | 40 | + | x | ) |
| = | 7200 | + | 180 | x | + | 9 2 | x | ( | 40 | + | x | ) |
| = | 7200 | + | 180 | x | + | 9 2 | x | × | 40 | + | 9 2 | x | x |
| = | 7200 | + | 180 | x | + | 180 | x | + | 9 2 | x | x |
| = | 7200 | + | 360 | x | + | 9 2 | x | x |
| 7200 | + | 360 | x | + | 9 2 | x | x | = | 642 |