Will bought 5 notebooks for $0.65 each. How much did the notebooks cost? plzz show your work

Based on what i know about mean, this doesn't add up.

Mr switzer needs to buy new 1-foot tiles to cover his bathroom floor. the floor is 12 feet long and 8 feet wide. each square foot of tile will cost $1.79. in dollars what will be the total cost of the tiles he needs to buy.

What is the name used to describe a graph where for some value of x, there exists 2 or more different values of y?