(b)
$General\ term,\ T_{r + 1} = \ ^{6}C_{r}x^{6 - r}\left( \frac{1}{x^{2}} \right)^{r}$
$\Longrightarrow T_{r + 1} = \ ^{6}C_{r}x^{6 - 3r}$
For term independent of $x,$ put
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 6 - 3r = 0$
$\Longrightarrow r = 2$
$\therefore$ Coefficient of independent term $= \ ^{6}C_{2} = 15$