| 39 | ÷ | ( | 39 | − | x | ) | ÷ | 9 10 | = | 21 10 |
| 方程两边同时乘以: | ( | 39 | − | x | ) |
| 39 | ÷ | 9 10 | = | 21 10 | ( | 39 | − | x | ) |
| 39 | ÷ | 9 10 | = | 21 10 | × | 39 | − | 21 10 | x |
130 3 | = | 819 10 | − | 21 10 | x |
21 10 | x | = | 819 10 | − | 130 3 |
21 10 | x | = | 1157 30 |
| x | = | 1157 30 | ÷ | 21 10 |
| = | 1157 30 | × | 10 21 |
| = | 1157 3 | × | 1 21 |
| x | = | 1157 63 |
| x | = | 18.365079 |