| 4 | ( | 15 | ÷ | ( | 7 | x | + | 18 | ) | + | 9 | ) | + | 3 | = | 19 |
| 4 | × | 15 | ÷ | ( | 7 | x | + | 18 | ) | + | 4 | × | 9 | + | 3 | = | 19 |
| 60 | ÷ | ( | 7 | x | + | 18 | ) | + | 36 | + | 3 | = | 19 |
| 60 | ÷ | ( | 7 | x | + | 18 | ) | + | 39 | = | 19 |
| 方程两边同时乘以: | ( | 7 | x | + | 18 | ) |
| 60 | + | 39 | ( | 7 | x | + | 18 | ) | = | 19 | ( | 7 | x | + | 18 | ) |
| 60 | + | 39 | × | 7 | x | + | 39 | × | 18 | = | 19 | ( | 7 | x | + | 18 | ) |
| 60 | + | 39 | × | 7 | x | + | 39 | × | 18 | = | 19 | × | 7 | x | + | 19 | × | 18 |
| 60 | + | 273 | x | + | 702 | = | 133 | x | + | 342 |
| 762 | + | 273 | x | = | 133 | x | + | 342 |
| 273 | x | − | 133 | x | = | 342 | − | 762 |
| 140 | x | = | 342 | − | 762 |
| 140 | x | = | - | 420 |
| x | = | - | 420 | ÷ | 140 |
| = | - | 420 | × | 1 140 |
| = | - | 3 | × | 1 |
| x | = | - | 3 |