| ( | 350 | − | 200 | ) | ÷ | ( | 500 | − | 350 | ) | = | ( | A | − | 9 | ) | ÷ | ( | 209 10 | − | A | ) |
| Multiply both sides of the equation by: | ( | 500 | − | 350 | ) | , | ( | 209 10 | − | A | ) |
| ( | 350 | − | 200 | ) | ( | 209 10 | − | A | ) | = | ( | A | − | 9 | ) | ( | 500 | − | 350 | ) |
| 350 | ( | 209 10 | − | A | ) | − | 200 | ( | 209 10 | − | A | ) | = | ( | A | − | 9 | ) | ( | 500 | − | 350 | ) |
| 350 | ( | 209 10 | − | A | ) | − | 200 | ( | 209 10 | − | A | ) | = | A | ( | 500 | − | 350 | ) | − | 9 | ( | 500 | − | 350 | ) |
| 350 | × | 209 10 | − | 350 | A | − | 200 | ( | 209 10 | − | A | ) | = | A | ( | 500 | − | 350 | ) | − | 9 | ( | 500 | − | 350 | ) |
| 350 | × | 209 10 | − | 350 | A | − | 200 | ( | 209 10 | − | A | ) | = | A | × | 500 | − | A | × | 350 | − | 9 | ( | 500 | − | 350 | ) |
| 7315 | − | 350 | A | − | 200 | ( | 209 10 | − | A | ) | = | A | × | 500 | − | A | × | 350 | − | 9 | ( | 500 | − | 350 | ) |
| 7315 | − | 350 | A | − | 200 | ( | 209 10 | − | A | ) | = | 150 | A | − | 9 | ( | 500 | − | 350 | ) |
| 7315 | − | 350 | A | − | 200 | × | 209 10 | + | 200 | A | = | 150 | A | − | 9 | ( | 500 | − | 350 | ) |
| 7315 | − | 350 | A | − | 200 | × | 209 10 | + | 200 | A | = | 150 | A | − | 9 | × | 500 | + | 9 | × | 350 |
| 7315 | − | 350 | A | − | 4180 | + | 200 | A | = | 150 | A | − | 4500 | + | 3150 |
| 3135 | − | 150 | A | = | 150 | A | − | 1350 |
| - | 150 | A | − | 150 | A | = | - | 1350 | − | 3135 |
| - | 300 | A | = | - | 1350 | − | 3135 |
| - | 300 | A | = | - | 4485 |
| 4485 | = | 300 | A |
| 300 | A | = | 4485 |
| A | = | 4485 | ÷ | 300 |
| = | 4485 | × | 1 300 |
| = | 299 | × | 1 20 |
| A | = | 299 20 |
| A | = | 14.95 |