Plz help me on dis

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?

The anwser cause i do not understand just plez

The circle below is centered at the point (3, 1) and has a radius of length 2. what is the equation?