A couple have 3 children. The age of elder son is not more than 20 years old and the difference between the ages of elder and younger son is multiple of 9. The age of elder son is two times the age of younger son and the sum of their ages is a perfect cube. Find the age of elder son and younger son.
1
9 years, 18 years
2
18 years, 9 years
3
8 years, 16 years
4
7 years, 14 years