| ( | 80 | + | 2 | x | ) | ( | 50 | + | 2 | x | ) | = | 5400 |
| 方程左边 = | 80 | ( | 50 | + | 2 | x | ) | + | 2 | x | ( | 50 | + | 2 | x | ) |
| = | 80 | × | 50 | + | 80 | × | 2 | x | + | 2 | x | ( | 50 | + | 2 | x | ) |
| = | 4000 | + | 160 | x | + | 2 | x | ( | 50 | + | 2 | x | ) |
| = | 4000 | + | 160 | x | + | 2 | x | × | 50 | + | 2 | x | × | 2 | x |
| = | 4000 | + | 160 | x | + | 100 | x | + | 4 | x | x |
| = | 4000 | + | 260 | x | + | 4 | x | x |
| 4000 | + | 260 | x | + | 4 | x | x | = | 5400 |