A company has determined that its weekly profit is a function of the number of items that it sells. Which equation could represent the weekly profit in thousands of dollars, y , when the company sells x items?

For profit to be a function of the number of items, each value of x must give exactly one value of y. Choice B directly gives one value of y for each x: y = −x² + 50x − 300. The equations involving y² can give two possible profit values for the same x, while choice D gives x in terms of y rather than a unique y for every x.

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