| 3 | x | + | ( | 25 | − | x | ) | × | 3 | × | 13 10 | = | 831 10 |
| 方程左边 = | 3 | x | + | ( | 25 | − | x | ) | × | 39 10 |
| 3 | x | + | ( | 25 | − | x | ) | × | 39 10 | = | 831 10 |
| 方程左边 = | 3 | x | + | 25 | × | 39 10 | − | x | × | 39 10 |
| = | 3 | x | + | 195 2 | − | x | × | 39 10 |
| = | - | 9 10 | x | + | 195 2 |
| - | 9 10 | x | + | 195 2 | = | 831 10 |
| - | 9 10 | x | = | 831 10 | − | 195 2 |
| - | 9 10 | x | = | - | 72 5 |
72 5 | = | 9 10 | x |
9 10 | x | = | 72 5 |
| x | = | 72 5 | ÷ | 9 10 |
| = | 72 5 | × | 10 9 |
| = | 8 | × | 2 |
| x | = | 16 |