If the sub total is 5.00 and tax is 5% how much is tax

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?

Ineed with math stuff it involves graphs

286 divided by 457.6 what is the quotient?