| 12 | + | 3 100 | x | + | 3 10 | × | 1 5 | x | = | 3 10 | × | 1 2 | x |
| Left side of the equation = | 12 | + | 3 100 | x | + | 3 50 | x |
| = | 12 | + | 9 100 | x |
| 12 | + | 9 100 | x | = | 3 10 | × | 1 2 | x |
| Right side of the equation = | 3 20 | x |
| 12 | + | 9 100 | x | = | 3 20 | x |
9 100 | x | − | 3 20 | x | = | - | 12 |
| - | 3 50 | x | = | - | 12 |
| 12 | = | 3 50 | x |
3 50 | x | = | 12 |
| x | = | 12 | ÷ | 3 50 |
| = | 12 | × | 50 3 |
| = | 4 | × | 50 |
| x | = | 200 |