| ( | 800 | − | 500 | ) | ÷ | ( | 1000 | − | 800 | ) | = | ( | A | − | 4 100 | ) | ÷ | ( | 19 500 | − | A | ) |
| Multiply both sides of the equation by: | ( | 1000 | − | 800 | ) | , | ( | 19 500 | − | A | ) |
| ( | 800 | − | 500 | ) | ( | 19 500 | − | A | ) | = | ( | A | − | 4 100 | ) | ( | 1000 | − | 800 | ) |
| 800 | ( | 19 500 | − | A | ) | − | 500 | ( | 19 500 | − | A | ) | = | ( | A | − | 4 100 | ) | ( | 1000 | − | 800 | ) |
| 800 | ( | 19 500 | − | A | ) | − | 500 | ( | 19 500 | − | A | ) | = | A | ( | 1000 | − | 800 | ) | − | 4 100 | ( | 1000 | − | 800 | ) |
| 800 | × | 19 500 | − | 800 | A | − | 500 | ( | 19 500 | − | A | ) | = | A | ( | 1000 | − | 800 | ) | − | 4 100 | ( | 1000 | − | 800 | ) |
| 800 | × | 19 500 | − | 800 | A | − | 500 | ( | 19 500 | − | A | ) | = | A | × | 1000 | − | A | × | 800 | − | 4 100 | ( | 1000 | − | 800 | ) |
152 5 | − | 800 | A | − | 500 | ( | 19 500 | − | A | ) | = | A | × | 1000 | − | A | × | 800 | − | 4 100 | ( | 1000 | − | 800 | ) |
152 5 | − | 800 | A | − | 500 | ( | 19 500 | − | A | ) | = | 200 | A | − | 4 100 | ( | 1000 | − | 800 | ) |
152 5 | − | 800 | A | − | 500 | × | 19 500 | + | 500 | A | = | 200 | A | − | 4 100 | ( | 1000 | − | 800 | ) |
152 5 | − | 800 | A | − | 500 | × | 19 500 | + | 500 | A | = | 200 | A | − | 4 100 | × | 1000 | + | 4 100 | × | 800 |
152 5 | − | 800 | A | − | 19 | + | 500 | A | = | 200 | A | − | 40 | + | 32 |
57 5 | − | 300 | A | = | 200 | A | − | 8 |
| - | 300 | A | − | 200 | A | = | - | 8 | − | 57 5 |
| - | 500 | A | = | - | 8 | − | 57 5 |
| - | 500 | A | = | - | 97 5 |
97 5 | = | 500 | A |
| 500 | A | = | 97 5 |
| A | = | 97 5 | ÷ | 500 |
| = | 97 5 | × | 1 500 |
| A | = | 97 2500 |
| A | = | 0.0388 |