If I was 7 when my sister was 16 and my brother was 8 when she is 19 how many more years will it take my brother to reach 21 when I'm 13?
I am 9 years younger than my sister, and my brother is 11 years younger than her, so he is two years younger than me. When I'm 13, I'll need 8 years to reach 21, so he'll require two years more: TEN YEARS.