Answer:
20 years
Explanation:
9=x
8=x+15
7=x+15+15
6=x+15+15+15
5=x+15+15+15+15
4=x+15+15+15+15+15
3=x+15+15+15+15+15+15
2=x+15+15+15+15+15+15+15
1=x+15+15+15+15+15+15+15+15
Xx6=6x
6x=x+15+15+15+15+15+15+15+15
6x=120
divide both sides by 6 to get X as 20
we had written the age of the youngest son as X so the youngest son is 20 years old.