OpenSAT

To solve for $x$, we can subtract $3x$ from both sides of the equation. This gives us $-12 = 3x + 3$. Subtracting 3 from both sides gives us $-15 = 3x$. Dividing both sides by 3 gives us $-5 = x$. This means $x$ must be equal to $-5$. The only choice that gives a result of $-5$ when solved for $x$ is choice C. Solving $-3x = 9$ for $x$ gives us $x = -3$, which is not correct.