let x = age of younger bro
ley y = age of older bro
x/y = 2/3 ----> x = 2y/3 eq.1
x+8 / y+8 = 3/4 eq.2
sub eq.1 into eq.2:
(2y/3) + 8 / y+8 = 3/4
(2y+24)/3 / y+8 = 3/4
2y + 24 / 3(y+8) = 3/4
2y+24 / 3y+24 = 3/4
4(2y+24) = 3(3y+24)
8y+96 = 9y+72
24=y
x=2y/3=2*24/3=16
Source- https://answers.yahoo.com/question/index?qid=20090519120852AA85lSu