Consider the function represented by 9x plus 3y is equal to 12 with x as the independent variable. How can this function be written using function notation?

Since x is the independent variable, solve the equation for y and write y as f(x). From 9x + 3y = 12, subtract 9x to get 3y = 12 − 9x, then divide by 3: y = 4 − 3x. Thus f(x) = −3x + 4, which is choice A.

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