Question

This is really difficult for me. If someone could help me I would really appreciate it.

Answer 1

Since we can add up the factors of 28 (excluding 28 itself) to get
1+2+4+7+14 = 28
this means that 28 is a perfect number. In the interval from 20 to 30, it is the only perfect number.

Answer: 28

Note: Something like 22 is not a perfect number since
1+2+11 = 14
which isn't 22 like we want. Every number, in the interval from 20 to 30, but 28 has this problem. 

Answer 2

20, 21, 22, 24, 25, 26, 27, 28, 30. hope that helped