Greg bikes 9 miles and swims 4 miles each week. he multiplied 5x10 to find how many more miles he bikes then swam in the last 10 weeks. does that make sense why or why not

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?