| ( | 12 | + | x | ) | ÷ | ( | 200 | + | x | ) | = | 1 5 |
| Multiply both sides of the equation by: | ( | 200 | + | x | ) |
| ( | 12 | + | x | ) | = | 1 5 | ( | 200 | + | x | ) |
| 12 | + | x | = | 1 5 | ( | 200 | + | x | ) |
| 12 | + | x | = | 1 5 | × | 200 | + | 1 5 | x |
| 12 | + | x | = | 40 | + | 1 5 | x |
| x | − | 1 5 | x | = | 40 | − | 12 |
4 5 | x | = | 40 | − | 12 |
4 5 | x | = | 28 |
| x | = | 28 | ÷ | 4 5 |
| = | 28 | × | 5 4 |
| = | 7 | × | 5 |
| x | = | 35 |