Given a= {(2,,,-,3)} a is a subset of a. n x r b. r x n c. n x n d. r x r

Last month, a 770 g box of cereal was sold at a grocery store for $3.10. however, this month, the cereal manufacturer launched the same cereal in a 640 g box, which is being sold at $2.50. what is the percent change in the unit price?