The age of each twin is $(32-8) \div 3 =8$ years old. Thus, Alex is $8 +8 =16$ years old. 
Alex is $8$ years older than her two sisters who are twins. The sum of the ages of all three girls is $32$ years old. How old is Alex? ($2007$ Math Kangaroo Problem, Level $5$-$6$, Question \#$9$) 

a) $$12$$ 
b) $$18$$ 
c) $$16$$ 
d) $$20$$ 
e) $$14$$ 