| ( | 400 | − | 200 | ) | ÷ | ( | 500 | − | 400 | ) | = | ( | B | − | 9 | ) | ÷ | ( | 209 10 | − | B | ) |
| Multiply both sides of the equation by: | ( | 500 | − | 400 | ) | , | ( | 209 10 | − | B | ) |
| ( | 400 | − | 200 | ) | ( | 209 10 | − | B | ) | = | ( | B | − | 9 | ) | ( | 500 | − | 400 | ) |
| 400 | ( | 209 10 | − | B | ) | − | 200 | ( | 209 10 | − | B | ) | = | ( | B | − | 9 | ) | ( | 500 | − | 400 | ) |
| 400 | ( | 209 10 | − | B | ) | − | 200 | ( | 209 10 | − | B | ) | = | B | ( | 500 | − | 400 | ) | − | 9 | ( | 500 | − | 400 | ) |
| 400 | × | 209 10 | − | 400 | B | − | 200 | ( | 209 10 | − | B | ) | = | B | ( | 500 | − | 400 | ) | − | 9 | ( | 500 | − | 400 | ) |
| 400 | × | 209 10 | − | 400 | B | − | 200 | ( | 209 10 | − | B | ) | = | B | × | 500 | − | B | × | 400 | − | 9 | ( | 500 | − | 400 | ) |
| 8360 | − | 400 | B | − | 200 | ( | 209 10 | − | B | ) | = | B | × | 500 | − | B | × | 400 | − | 9 | ( | 500 | − | 400 | ) |
| 8360 | − | 400 | B | − | 200 | ( | 209 10 | − | B | ) | = | 100 | B | − | 9 | ( | 500 | − | 400 | ) |
| 8360 | − | 400 | B | − | 200 | × | 209 10 | + | 200 | B | = | 100 | B | − | 9 | ( | 500 | − | 400 | ) |
| 8360 | − | 400 | B | − | 200 | × | 209 10 | + | 200 | B | = | 100 | B | − | 9 | × | 500 | + | 9 | × | 400 |
| 8360 | − | 400 | B | − | 4180 | + | 200 | B | = | 100 | B | − | 4500 | + | 3600 |
| 4180 | − | 200 | B | = | 100 | B | − | 900 |
| - | 200 | B | − | 100 | B | = | - | 900 | − | 4180 |
| - | 300 | B | = | - | 900 | − | 4180 |
| - | 300 | B | = | - | 5080 |
| 5080 | = | 300 | B |
| 300 | B | = | 5080 |
| B | = | 5080 | ÷ | 300 |
| = | 5080 | × | 1 300 |
| = | 254 | × | 1 15 |
| B | = | 254 15 |
| B | = | 16.933333 |