| ( | 15 | + | x | ) | × | 3 | ÷ | 5 | + | 15 | × | 2 | + | 5 2 | x | = | 109 2 |
| 方程左边 = | ( | 15 | + | x | ) | × | 3 5 | + | 30 | + | 5 2 | x |
| ( | 15 | + | x | ) | × | 3 5 | + | 30 | + | 5 2 | x | = | 109 2 |
| 方程左边 = | 15 | × | 3 5 | + | x | × | 3 5 | + | 30 | + | 5 2 | x |
| = | 9 | + | x | × | 3 5 | + | 30 | + | 5 2 | x |
| = | 39 | + | 31 10 | x |
| 39 | + | 31 10 | x | = | 109 2 |
31 10 | x | = | 109 2 | − | 39 |
31 10 | x | = | 31 2 |
| x | = | 31 2 | ÷ | 31 10 |
| = | 31 2 | × | 10 31 |
| = | 1 | × | 5 |
| x | = | 5 |