| 12 | × | 30 | + | 16 | ( | 20 | − | m | ) | = | 13 | × | 30 | + | 14 | ( | 20 | − | m | ) |
| 方程左边 = | 360 | + | 16 | ( | 20 | − | m | ) |
| 360 | + | 16 | ( | 20 | − | m | ) | = | 13 | × | 30 | + | 14 | ( | 20 | − | m | ) |
| 方程左边 = | 360 | + | 16 | × | 20 | − | 16 | m |
| = | 360 | + | 320 | − | 16 | m |
| = | 680 | − | 16 | m |
| 680 | − | 16 | m | = | 13 | × | 30 | + | 14 | ( | 20 | − | m | ) |
| 方程右边 = | 390 | + | 14 | ( | 20 | − | m | ) |
| 680 | − | 16 | m | = | 390 | + | 14 | ( | 20 | − | m | ) |
| 方程右边 = | 390 | + | 14 | × | 20 | − | 14 | m |
| = | 390 | + | 280 | − | 14 | m |
| = | 670 | − | 14 | m |
| 680 | − | 16 | m | = | 670 | − | 14 | m |
| - | 16 | m | + | 14 | m | = | 670 | − | 680 |
| - | 2 | m | = | 670 | − | 680 |
| - | 2 | m | = | - | 10 |
| 10 | = | 2 | m |
| 2 | m | = | 10 |
| m | = | 10 | ÷ | 2 |
| = | 10 | × | 1 2 |
| = | 5 | × | 1 |
| m | = | 5 |