2009 AMC 12A Problem 9

Note that $a + b + c = f(1).$ Using $f(x + 3) = 3x^2 + 7x + 4$ with $x = -2$ gives $$\begin{aligned} f(1) &= f(-2 + 3) \\ &= 3(-2)^2 + 7(-2) + 4 \\ &= 12 - 14 + 4 = 2. \end{aligned}$$ Thus, the correct answer is D.