What is the relationship between Za and Zb?

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?

How to simply and write the answer n a whole number

Find the missing factor. write your answer inexponential form.9^2=9^4×