To find the missing number in the equivalent ratio \( \frac{\text{blank}}{12} \) that is equivalent to \( \frac{12}{4} \), we can first simplify \( \frac{12}{4} \):
\[ \frac{12}{4} = 3 \]
Now, to find an equivalent ratio, we will set up the equivalent ratio \( \frac{3}{1} \) (since 3 is the simplified form of \( \frac{12}{4} \)) and express it in terms of the new ratio \( \frac{x}{12} \):
To find \( x \), we can set up the proportion:
\[ \frac{3}{1} = \frac{x}{12} \]
Now, cross-multiply:
\[ 3 \cdot 12 = 1 \cdot x \]
This simplifies to:
\[ 36 = x \]
Thus, the missing number is \( 36 \).