To find out what number 4 is 16% of, you can set up the equation:
\[ 4 = 0.16 \times x \]
where \( x \) is the number we want to find. To solve for \( x \), divide both sides by 0.16:
\[ x = \frac{4}{0.16} \]
Calculating this gives:
\[ x = 25 \]
So, 4 is 16% of 25.