| ( | 20 | − | 5 | t | ) | ( | 15 | − | 6 | t | ) | = | 60 | t |
| 方程左边 = | 20 | ( | 15 | − | 6 | t | ) | − | 5 | t | ( | 15 | − | 6 | t | ) |
| = | 20 | × | 15 | − | 20 | × | 6 | t | − | 5 | t | ( | 15 | − | 6 | t | ) |
| = | 300 | − | 120 | t | − | 5 | t | ( | 15 | − | 6 | t | ) |
| = | 300 | − | 120 | t | − | 5 | t | × | 15 | + | 5 | t | × | 6 | t |
| = | 300 | − | 120 | t | − | 75 | t | + | 30 | t | t |
| = | 300 | − | 195 | t | + | 30 | t | t |
| 300 | − | 195 | t | + | 30 | t | t | = | 60 | t |