The vertex of the angle below is the center of the circle. Find n if n% of the circle is shaded. Give your answer as a mixed fraction.

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?