Solve for x. Help me out because I haven’t been paying attention all year pt.2

For each proportion find the unknown number x 1/5/8=×/15

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?

Is there an x intercept in the equation 60*1.15^x