To solve the equation \( \frac{x}{12} = 6 \) for \( x \), you should multiply both sides of the equation by 12.
Here's how it looks:
\[ \frac{x}{12} \times 12 = 6 \times 12 \]
This simplifies to:
\[ x = 72 \]
So the correct option is to multiply by 12.