Currently, Brian is 8 years old, and since his brother is twice his age, his brother is 2 times 8, which makes him 16 years old right now.
As time goes on, both of them will age at the same rate. When Brian turns 11, he will be 3 years older than he is now (from 8 to 11). Therefore, we need to add those 3 years to his brother’s current age as well.
So, if we add 3 years to his brother’s current age of 16, we find that his brother will be 16 + 3 = 19 years old when Brian turns 11.
In summary, when Brian is 11 years old, his brother will be 19 years old.