1 200 | × | 400 | ÷ | ( | 400 | + | x | ) | + | x | ÷ | ( | 400 | + | x | ) | × | 4 100 | = | 0 |
| Multiply both sides of the equation by: | ( | 400 | + | x | ) |
1 200 | × | 400 | + | x | × | 4 100 | = | 0 |
| x | × | 4 100 | = | 0 | − | 1 200 | × | 400 |
| x | × | 4 100 | = | 0 | − | 2 |
4 100 | x | = | - | 2 |
| x | = | - | 2 | ÷ | 4 100 |
| = | - | 2 | × | 100 4 |
| = | - | 1 | × | 100 2 |
| x | = | - | 100 2 |
| x | = | - | 50 |