| ( | 800 | − | 500 | ) | ÷ | ( | 1000 | − | 800 | ) | = | ( | A | − | 4 | ) | ÷ | ( | 19 5 | − | A | ) |
| Multiply both sides of the equation by: | ( | 1000 | − | 800 | ) | , | ( | 19 5 | − | A | ) |
| ( | 800 | − | 500 | ) | ( | 19 5 | − | A | ) | = | ( | A | − | 4 | ) | ( | 1000 | − | 800 | ) |
| 800 | ( | 19 5 | − | A | ) | − | 500 | ( | 19 5 | − | A | ) | = | ( | A | − | 4 | ) | ( | 1000 | − | 800 | ) |
| 800 | ( | 19 5 | − | A | ) | − | 500 | ( | 19 5 | − | A | ) | = | A | ( | 1000 | − | 800 | ) | − | 4 | ( | 1000 | − | 800 | ) |
| 800 | × | 19 5 | − | 800 | A | − | 500 | ( | 19 5 | − | A | ) | = | A | ( | 1000 | − | 800 | ) | − | 4 | ( | 1000 | − | 800 | ) |
| 800 | × | 19 5 | − | 800 | A | − | 500 | ( | 19 5 | − | A | ) | = | A | × | 1000 | − | A | × | 800 | − | 4 | ( | 1000 | − | 800 | ) |
| 3040 | − | 800 | A | − | 500 | ( | 19 5 | − | A | ) | = | A | × | 1000 | − | A | × | 800 | − | 4 | ( | 1000 | − | 800 | ) |
| 3040 | − | 800 | A | − | 500 | ( | 19 5 | − | A | ) | = | 200 | A | − | 4 | ( | 1000 | − | 800 | ) |
| 3040 | − | 800 | A | − | 500 | × | 19 5 | + | 500 | A | = | 200 | A | − | 4 | ( | 1000 | − | 800 | ) |
| 3040 | − | 800 | A | − | 500 | × | 19 5 | + | 500 | A | = | 200 | A | − | 4 | × | 1000 | + | 4 | × | 800 |
| 3040 | − | 800 | A | − | 1900 | + | 500 | A | = | 200 | A | − | 4000 | + | 3200 |
| 1140 | − | 300 | A | = | 200 | A | − | 800 |
| - | 300 | A | − | 200 | A | = | - | 800 | − | 1140 |
| - | 500 | A | = | - | 800 | − | 1140 |
| - | 500 | A | = | - | 1940 |
| 1940 | = | 500 | A |
| 500 | A | = | 1940 |
| A | = | 1940 | ÷ | 500 |
| = | 1940 | × | 1 500 |
| = | 97 | × | 1 25 |
| A | = | 97 25 |
| A | = | 3.88 |