| 6 | x | + | 4 | x | − | 39 | = | 81 |
| 方程左边 = | 10 | x | − | 39 |
| 10 | x | − | 39 | = | 81 |
| 10 | x | = | 81 | + | 39 |
| 10 | x | = | 120 |
| x | = | 120 | ÷ | 10 |
| = | 120 | × | 1 10 |
| = | 12 | × | 1 |
| x | = | 12 |
| 3 | x | + | 5 | x | + | 23 | = | 79 |
| 方程左边 = | 8 | x | + | 23 |
| 8 | x | + | 23 | = | 79 |
| 8 | x | = | 79 | − | 23 |
| 8 | x | = | 56 |
| x | = | 56 | ÷ | 8 |
| = | 56 | × | 1 8 |
| = | 7 | × | 1 |
| x | = | 7 |
| 5 | x | + | 21 | = | 61 | + | x |
| 5 | x | − | x | = | 61 | − | 21 |
| 4 | x | = | 61 | − | 21 |
| 4 | x | = | 40 |
| x | = | 40 | ÷ | 4 |
| = | 40 | × | 1 4 |
| = | 10 | × | 1 |
| x | = | 10 |
| 8 | x | + | 2 | x | + | 21 | = | 141 |
| 方程左边 = | 10 | x | + | 21 |
| 10 | x | + | 21 | = | 141 |
| 10 | x | = | 141 | − | 21 |
| 10 | x | = | 120 |
| x | = | 120 | ÷ | 10 |
| = | 120 | × | 1 10 |
| = | 12 | × | 1 |
| x | = | 12 |
| 2 | x | + | 22 | = | 30 | + | x |
| 2 | x | − | x | = | 30 | − | 22 |
| x | = | 30 | − | 22 |
| x | = | 30 | − | 22 |
| x | = | 8 |