let g be a translation 4 units down and a horizontal shrink by a factor of 1/4 of the graph of f(x)=x

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?