Answer
See the proof below.
Work Step by Step
We have $$ |3 x-12|=3|x-4| $$
Since $|3x-12| $ is a multiple of $|x-4|$, then we see that $|3x-12| $ is small by taking $ x $ sufficiently close to $4 $. Hence, we have $$ \lim _{x \rightarrow 4} 3x=12.$$
