| 29 | × | 100 | ÷ | x | ÷ | 21 20 | ÷ | 90 | × | 100 | = | 42 |
| 方程两边同时乘以: | x |
| 29 | × | 100 | ÷ | 21 20 | ÷ | 90 | × | 100 | = | 42 | x |
| - | 42 | x | = | - | 29 | × | 100 | ÷ | 21 20 | ÷ | 90 | × | 100 |
| - | 42 | x | = | - | 580000 189 |
580000 189 | = | 42 | x |
| 42 | x | = | 580000 189 |
| x | = | 580000 189 | ÷ | 42 |
| = | 580000 189 | × | 1 42 |
| = | 290000 189 | × | 1 21 |
| x | = | 290000 3969 |
| x | = | 73.066264 |