Roger likes to eat Crunchy Flakes cereal for breakfast every morning. Crunchy Flakes comes in a 20-ounce box that costs $4.20 and a 30-ounce box that costs $6.00. Which is the better buy? (HINT: Find which one is less per ounce)

A. 20-ounce box

B. 30-ounce box

C. they both are the same per ounce