To multiply \(-9 \frac{1}{2}\) by \(0.04\), we first convert \(-9 \frac{1}{2}\) into an improper fraction.
\[ -9 \frac{1}{2} = -\left(9 \times 2 + 1\right)/2 = -\frac{19}{2} \]
Now we multiply \(-\frac{19}{2}\) by \(0.04\):
\[ -\frac{19}{2} \times 0.04 \]
Convert \(0.04\) to a fraction:
\[ 0.04 = \frac{4}{100} = \frac{1}{25} \]
Now perform the multiplication:
\[ -\frac{19}{2} \times \frac{1}{25} = -\frac{19 \cdot 1}{2 \cdot 25} = -\frac{19}{50} \]
Now we need to convert \(-\frac{19}{50}\) to a decimal:
\[ -\frac{19}{50} = -0.38 \]
Thus, the final result is:
\[ \boxed{-0.38} \]
Therefore, the answer is B: \(-0.38\).