Adam, Jan and Stas were $(24-4)\div4=5$ years old three years ago. Marysia was $5+4=9$ years old. Thus, Marysia is $9+3=12$ years old. 
The triplets Adam, Jan and Stas and their sister Marysia who is four years older than them were $24$ years old together three years ago. How old is Marysia today? (2001 Math Kangaroo Problem, Level 5-6, Question \#18) 
A. $$5$$ 
B. $$8$$ 
C. $$9$$ 
D. $$12$$ 
E. $$15$$ 