| 3 | ( | 5 | y | − | 11 | ) | ÷ | 2 | + | 5 | y | = | 21 |
| 方程左边 = | 3 2 | ( | 5 | y | − | 11 | ) | + | 5 | y |
3 2 | ( | 5 | y | − | 11 | ) | + | 5 | y | = | 21 |
| 方程左边 = | 3 2 | × | 5 | y | − | 3 2 | × | 11 | + | 5 | y |
| = | 15 2 | y | − | 33 2 | + | 5 | y |
| = | 25 2 | y | − | 33 2 |
25 2 | y | − | 33 2 | = | 21 |
25 2 | y | = | 21 | + | 33 2 |
25 2 | y | = | 75 2 |
| y | = | 75 2 | ÷ | 25 2 |
| = | 75 2 | × | 2 25 |
| = | 3 | × | 1 |
| y | = | 3 |