| ( | 40 | + | m | − | 30 | ) | ( | 600 | − | 10 | m | ) | = | 10000 |
| 方程左边 = | 40 | ( | 600 | − | 10 | m | ) | + | m | ( | 600 | − | 10 | m | ) | − | 30 | ( | 600 | − | 10 | m | ) |
| = | 40 | × | 600 | − | 40 | × | 10 | m | + | m | ( | 600 | − | 10 | m | ) | − | 30 | ( | 600 | − | 10 | m | ) |
| = | 24000 | − | 400 | m | + | m | ( | 600 | − | 10 | m | ) | − | 30 | ( | 600 | − | 10 | m | ) |
| = | 24000 | − | 400 | m | + | m | × | 600 | − | m | × | 10 | m | − | 30 | ( | 600 | − | 10 | m | ) |
| = | 24000 | + | 200 | m | − | m | × | 10 | m | − | 30 | ( | 600 | − | 10 | m | ) |
| = | 24000 | + | 200 | m | − | m | × | 10 | m | − | 30 | × | 600 | + | 30 | × | 10 | m |
| = | 24000 | + | 200 | m | − | m | × | 10 | m | − | 18000 | + | 300 | m |
| = | 6000 | + | 500 | m | − | m | × | 10 | m |
| 6000 | + | 500 | m | − | m | × | 10 | m | = | 10000 |