At a school prize giving day the number of men was half of women. The number of children was three times that of women. The number of women who attended was 3x. What was the sum of the men and children?
women -- 3x
men ---- 3x/2
children -- 9x
men + children = 3x/2 + 9x
= 3x/2 + 18x/2 = 21x/2