A fair coin is tossed three times. Let \( X \) be the number of tails appearing and its distribution is:
\[
\begin{array}{|c|c|c|c|c|}
\hline
X = x & 0 & 1 & 2 & 3 \\
\hline
P(X = x) & \frac{1}{8} & \frac{3}{8} & \frac{3}{8} & \frac{1}{8} \\
\hline
\end{array}
\]
Then the variance of \( X \) is: