| ( | 84 | + | a | ) | ÷ | ( | 70 | + | a | ) | = | 11 10 |
| Multiply both sides of the equation by: | ( | 70 | + | a | ) |
| ( | 84 | + | a | ) | = | 11 10 | ( | 70 | + | a | ) |
| 84 | + | a | = | 11 10 | ( | 70 | + | a | ) |
| 84 | + | a | = | 11 10 | × | 70 | + | 11 10 | a |
| 84 | + | a | = | 77 | + | 11 10 | a |
| a | − | 11 10 | a | = | 77 | − | 84 |
| - | 1 10 | a | = | 77 | − | 84 |
| - | 1 10 | a | = | - | 7 |
| 7 | = | 1 10 | a |
1 10 | a | = | 7 |
| a | = | 7 | ÷ | 1 10 |
| = | 7 | × | 10 |
| a | = | 70 |