$(20-4)\div4=4$ 
John bought some cupcakes, and each of them cost $4$ dollars. He gave the salesperson $20$ dollars and got $4$ dollars as change. How many cupcakes did John buy? (Adapted from 2005 Math Kangaroo Problem, Level 3-4, Question \#3) 
(a) $$6$$ 
(b) $$8$$ 
(c) $$10$$ 
(d) $$5$$ 
(e) $$4$$ 