Use one of more properties to rewrite each expression as an expression that does not use parenthesis. 4 + (b + 0) =

PLease help will give branliest

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?