A store sells notebooks for 3 dollars 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 0, 1, 2, or more notebooks, so x must be a nonnegative integer. Each notebook costs $3, making the total y = 3x, which is also a nonnegative integer. Therefore, the best description is that x and y are both integers greater than or equal to 0.

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