| ( | ( | 7 | ÷ | 3 | ) | r | + | 10 | ) | ÷ | ( | r | + | 30 | ) | = | 4 | ÷ | 3 |
| Multiply both sides of the equation by: | ( | r | + | 30 | ) |
| ( | ( | 7 | ÷ | 3 | ) | r | + | 10 | ) | = | 4 | ÷ | 3 | × | ( | r | + | 30 | ) |
| ( | 7 | ÷ | 3 | ) | r | + | 10 | = | 4 | ÷ | 3 | × | ( | r | + | 30 | ) |
| ( | 7 | ÷ | 3 | ) | r | + | 10 | = | 4 | ÷ | 3 | × | r | + | 4 | ÷ | 3 | × | 30 |
| ( | 7 | ÷ | 3 | ) | r | + | 10 | = | 4 3 | r | + | 40 |
| 7 | ÷ | 3 | × | r | + | 10 | = | 4 3 | r | + | 40 |
7 3 | r | + | 10 | = | 4 3 | r | + | 40 |
7 3 | r | − | 4 3 | r | = | 40 | − | 10 |
| r | = | 40 | − | 10 |
| r | = | 40 | − | 10 |
| r | = | 30 |