| 225 | = | 21 20 | x | − | ( | 225 | − | ( | 21 20 | x | ) | ) |
| Right side of the equation = | 21 20 | x | − | 225 | + | ( | 21 20 | x | ) |
| = | 21 20 | x | − | 225 | + | 21 20 | x |
| = | 21 10 | x | − | 225 |
| 225 | = | 21 10 | x | − | 225 |
| - | 21 10 | x | = | - | 225 | − | 225 |
| - | 21 10 | x | = | - | 450 |
| 450 | = | 21 10 | x |
21 10 | x | = | 450 |
| x | = | 450 | ÷ | 21 10 |
| = | 450 | × | 10 21 |
| = | 150 | × | 10 7 |
| x | = | 1500 7 |
| x | = | 214.285714 |