A store sells notebooks for $3 each and does not charge sales tax. If x represents the number of notebooks Adele buys and y represents the total cost of the notebooks she buys, which best describes the values of x and y?

Adele can buy only a whole number of notebooks, so x must be a nonnegative integer, including 0 if she buys none. Each notebook costs $3, so y = 3x; therefore the total cost is also a nonnegative integer number of dollars. This matches the choice that both x and y are integers greater than or equal to 0.

AI-written and checked against the verified answer.