| ( | 370 | − | 200 | ) | ÷ | ( | 500 | − | 370 | ) | = | ( | A | − | 9 | ) | ÷ | ( | 209 10 | − | A | ) |
| Multiply both sides of the equation by: | ( | 500 | − | 370 | ) | , | ( | 209 10 | − | A | ) |
| ( | 370 | − | 200 | ) | ( | 209 10 | − | A | ) | = | ( | A | − | 9 | ) | ( | 500 | − | 370 | ) |
| 370 | ( | 209 10 | − | A | ) | − | 200 | ( | 209 10 | − | A | ) | = | ( | A | − | 9 | ) | ( | 500 | − | 370 | ) |
| 370 | ( | 209 10 | − | A | ) | − | 200 | ( | 209 10 | − | A | ) | = | A | ( | 500 | − | 370 | ) | − | 9 | ( | 500 | − | 370 | ) |
| 370 | × | 209 10 | − | 370 | A | − | 200 | ( | 209 10 | − | A | ) | = | A | ( | 500 | − | 370 | ) | − | 9 | ( | 500 | − | 370 | ) |
| 370 | × | 209 10 | − | 370 | A | − | 200 | ( | 209 10 | − | A | ) | = | A | × | 500 | − | A | × | 370 | − | 9 | ( | 500 | − | 370 | ) |
| 7733 | − | 370 | A | − | 200 | ( | 209 10 | − | A | ) | = | A | × | 500 | − | A | × | 370 | − | 9 | ( | 500 | − | 370 | ) |
| 7733 | − | 370 | A | − | 200 | ( | 209 10 | − | A | ) | = | 130 | A | − | 9 | ( | 500 | − | 370 | ) |
| 7733 | − | 370 | A | − | 200 | × | 209 10 | + | 200 | A | = | 130 | A | − | 9 | ( | 500 | − | 370 | ) |
| 7733 | − | 370 | A | − | 200 | × | 209 10 | + | 200 | A | = | 130 | A | − | 9 | × | 500 | + | 9 | × | 370 |
| 7733 | − | 370 | A | − | 4180 | + | 200 | A | = | 130 | A | − | 4500 | + | 3330 |
| 3553 | − | 170 | A | = | 130 | A | − | 1170 |
| - | 170 | A | − | 130 | A | = | - | 1170 | − | 3553 |
| - | 300 | A | = | - | 1170 | − | 3553 |
| - | 300 | A | = | - | 4723 |
| 4723 | = | 300 | A |
| 300 | A | = | 4723 |
| A | = | 4723 | ÷ | 300 |
| = | 4723 | × | 1 300 |
| A | = | 4723 300 |
| A | = | 15.743333 |