Question 451510
Let's mark the age of each brother with B1, B2, B3, B4

B1 = x     - youngest brother's age is x years
B2 = x + 2 - next brother is 2 years older then the youngest
B3 = x + 4 - next brother is 2 years older than the previous brother
B4 = x + 6 - next brother is 2 years older than the previous brother

Sum of all their ages is 36:

B1 + B2 + B3 + B4 = 36

x + (x + 2) + (x + 4) + (x + 6) = 36
x + x + 2 + x + 4 + x +6        = 36
4x + 12                         = 36
4x                              = 36 -12 = 24
x                               = 24/4
x                               = 6

Now when we know the age of the youngest brother we can find ages of all 4:

B1 = 6
B2 = 8
B3 = 10
B4 = 12

Check: 6 + 8 + 10 + 12 = 36