(b)
$\therefore P = P$(getting a head)$= \frac{1}{2}$
$\therefore\ q = \frac{1}{2}$
$\therefore$ Required probability
$= {\ ^{10}C}_{6}\left( \frac{1}{2} \right)^{6}\left( \frac{1}{2} \right)^{4}$
$= \frac{10!}{6!4!} \times \frac{1}{2^{10}} = \frac{105}{512}$