Suppose y varies directly with x. If y=6 when x=-2, find x when y=15

Which of the following tables represents exponential functions?

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?

Find an bif a = {3, 6, 9, 12) and b = {2, 4, 6, 8, 10).