If $3 x-9=12$, then the value of $6 x$ is
(A) 42
(B) 24
(C) 6
(D) 32
(E) 52
Since $3 x-9=12$, then $3 x=12+9=21$.

Since $3 x=21$, then $6 x=2(3 x)=2(21)=42$.

(Note that we did not need to determine the value of $x$.)

ANSWER: (A)