Add the 2/5, 3/4, 1/2

Me. i can't figure out this question. give an explanation too. .

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?

Finding tbe values of the variables in each kite