Use doubles to help you add 7+8

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?

What percent of 18 is 24? and plz explain thx.

What is the radius of the cone in the diagram? round your answer to the nearest whole number