| ( | 60 | + | m | − | 40 | ) | ( | 300 | − | 10 | m | ) | = | 2250 |
| 方程左边 = | 60 | ( | 300 | − | 10 | m | ) | + | m | ( | 300 | − | 10 | m | ) | − | 40 | ( | 300 | − | 10 | m | ) |
| = | 60 | × | 300 | − | 60 | × | 10 | m | + | m | ( | 300 | − | 10 | m | ) | − | 40 | ( | 300 | − | 10 | m | ) |
| = | 18000 | − | 600 | m | + | m | ( | 300 | − | 10 | m | ) | − | 40 | ( | 300 | − | 10 | m | ) |
| = | 18000 | − | 600 | m | + | m | × | 300 | − | m | × | 10 | m | − | 40 | ( | 300 | − | 10 | m | ) |
| = | 18000 | − | 300 | m | − | m | × | 10 | m | − | 40 | ( | 300 | − | 10 | m | ) |
| = | 18000 | − | 300 | m | − | m | × | 10 | m | − | 40 | × | 300 | + | 40 | × | 10 | m |
| = | 18000 | − | 300 | m | − | m | × | 10 | m | − | 12000 | + | 400 | m |
| = | 6000 | + | 100 | m | − | m | × | 10 | m |
| 6000 | + | 100 | m | − | m | × | 10 | m | = | 2250 |