| ( | 4 | + | m | ) | × | 5 | × | 6 | + | 120 | = | 12 | × | 25 |
| 方程左边 = | ( | 4 | + | m | ) | × | 30 | + | 120 |
| ( | 4 | + | m | ) | × | 30 | + | 120 | = | 12 | × | 25 |
| 方程左边 = | 4 | × | 30 | + | m | × | 30 | + | 120 |
| = | 120 | + | m | × | 30 | + | 120 |
| = | 240 | + | 30 | m |
| 240 | + | 30 | m | = | 12 | × | 25 |
| 方程右边 = | 300 |
| 240 | + | 30 | m | = | 300 |
| 30 | m | = | 300 | − | 240 |
| 30 | m | = | 60 |
| m | = | 60 | ÷ | 30 |
| = | 60 | × | 1 30 |
| = | 2 | × | 1 |
| m | = | 2 |