A5. Let $3 a+6=b$ and $3 b=9 c$. Then $c-a$ is:
(A) -2
(B) $\frac{1}{12}$
(C) 1
(D) 2
(E) 3
A5. Using the equality $b=3a+6$ in the second equation. This gives us $3a+6=3c$, from which we express $c-a=2$.