We know that he got 4.20$ for 4 candies so for one candy we do:
4.20/4= 1.05$ for one candy bar.
Explanation: to know the price of one candy bar you must divide the total cost of the 4 candies which is 4.20$, by the number of candies which is 4, and that gives you the cost of one candy which is 1.05 $.
