| 420 | = | 120 | + | 2 | × | 10 | × | 2 | + | 3 | × | 13 | + | ( | x | − | 1 2 | ) |
| Right side of the equation = | 120 | + | 40 | + | 39 | + | ( | x | − | 1 2 | ) |
| = | 199 | + | ( | x | − | 1 2 | ) |
| 420 | = | 199 | + | ( | x | − | 1 2 | ) |
| Right side of the equation = | 199 | + | x | − | 1 2 |
| = | 397 2 | + | x |
| 420 | = | 397 2 | + | x |
| - | x | = | 397 2 | − | 420 |
| - | x | = | - | 443 2 |
443 2 | = | x |
| x | = | 443 2 |