Algebra age question

Question

Currently, Noah is four years less than his brother Dougie. In seven years, the sum of their ages will be

40.

Answer 1

N=D-4

N+7 + D+7 = 40

N+D = 40-14 = 26

D-4 + D = 30

2D = 30

D = 30/2 = 15 years old for Dougie

N = 15-4 = 11 years old for Noah

in 7 years they are 22 and 18 = 40