When I was 4 years old my brother was half of my age. Now I’m 44, how old is my brother?

Let your age be a and your brother’s age be b when a=4

a-b= always a constant

When a=4, b=4/2=2

a-b=4–2=2=constant

Therefore,

44- your brother’s age= 2

Your brother’s age = 42 now