To cross multiply, we typically do it in the context of an equation involving a fraction, for example, \( \frac{a}{b} = \frac{c}{d} \).
In your case, you have just \( 3x = \), but it seems like you're missing a fraction on the other side of the equation to complete it. If you're looking to cross multiply with a specific equation, please provide the full equation. For example, if the equation were something like:
\[ \frac{3}{x} = \frac{1}{2} \]
Then you would cross multiply as follows:
\[ 3 \cdot 2 = 1 \cdot x \]
This simplifies to:
\[ 6 = x \]
If you provide the complete equation, I can assist you with the specific cross multiplication.