- \( g(3) = 81 \)
- \( g(6) = 648 \)
- \( g(4) = 192 \)
- \( g(8) = 1536 \)
- The value of \( g(x) \) increases by a factor of \( 8 \) when \( x \) doubles.
Thus, the final answers are:
\[
\boxed{g(3) = 81, \, g(6) = 648, \, g(4) = 192, \, g(8) = 1536, \, \text{factor} = 8}
\]