Which represents all the values of x that make the rational expression the fraction with numerator negative 6 x plus 42 and denominator 3 x plus 9 undefined?

A rational expression is undefined when its denominator equals zero. Set 3x + 9 = 0 and solve: 3x = −9, so x = −3. The numerator does not change where the expression is undefined, so the correct choice is x is equal to negative 3.

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