3c+-9=18 i don't know how to do this problems

Suppose the radius of a circle is 16. what issuppose the radius of a circle is 16. what is its circumference its circumference

15. if the 8% tax on an item amounts to $0.96, what is the final price (tax included) of the item?

Mrs. robinson bought a novel at a bookstore on sale for 20% off its regular price of $29.99. mr chang bought the same novel at a different bookstore for 10% off its regular price of $25. which person received the better discount?