21 20 | x | + | 5547 100 | + | 15 | + | 5 | + | ( | 21 20 | x | + | 5547 100 | + | 15 | + | 5 | ) | × | 3 20 | = | 420 |
| 方程左边 = | 21 20 | x | + | 7547 100 | + | ( | 21 20 | x | + | 5547 100 | + | 15 | + | 5 | ) | × | 3 20 |
21 20 | x | + | 7547 100 | + | ( | 21 20 | x | + | 5547 100 | + | 15 | + | 5 | ) | × | 3 20 | = | 420 |
| 方程左边 = | 21 20 | x | + | 7547 100 | + | 21 20 | x | × | 3 20 | + | 5547 100 | × | 3 20 | + | 15 | × | 3 20 | + | 5 | × | 3 20 |
| = | 21 20 | x | + | 7547 100 | + | 63 400 | x | + | 16641 2000 | + | 9 4 | + | 3 4 |
| = | 483 400 | x | + | 173581 2000 |
483 400 | x | + | 173581 2000 | = | 420 |
483 400 | x | = | 420 | − | 173581 2000 |
483 400 | x | = | 666419 2000 |
| x | = | 666419 2000 | ÷ | 483 400 |
| = | 666419 2000 | × | 400 483 |
| = | 666419 5 | × | 1 483 |
| x | = | 666419 2415 |
| x | = | 275.949896 |