| ( | 400 | × | 20 | + | 150 | x | ) | ÷ | ( | 20 | + | x | ) | = | 200 |
| Multiply both sides of the equation by: | ( | 20 | + | x | ) |
| ( | 400 | × | 20 | + | 150 | x | ) | = | 200 | ( | 20 | + | x | ) |
| 400 | × | 20 | + | 150 | x | = | 200 | ( | 20 | + | x | ) |
| 400 | × | 20 | + | 150 | x | = | 200 | × | 20 | + | 200 | x |
| 8000 | + | 150 | x | = | 4000 | + | 200 | x |
| 150 | x | − | 200 | x | = | 4000 | − | 8000 |
| - | 50 | x | = | 4000 | − | 8000 |
| - | 50 | x | = | - | 4000 |
| 4000 | = | 50 | x |
| 50 | x | = | 4000 |
| x | = | 4000 | ÷ | 50 |
| = | 4000 | × | 1 50 |
| = | 80 | × | 1 |
| x | = | 80 |