(d) $mg\sin{\theta = ma}$
$\therefore\ \ \ a = g\sin\theta$
Where $a$ is long the inclined plane.
$\therefore\ \ \ $Vertical component of acceleration is $g\ \sin^{2}\theta.$
$\therefore\ $ Relative vertical acceleration of A with respect to B is
$g\left( \sin^{2}\ 60{^\circ} - \sin^{2}30{^\circ} \right) = \frac{g}{2} = 4.9\ {ms}^{- 2}$
(in vertical direction)