(a) $Maximum\ height,\ H = \frac{u^{2}\sin^{2}\theta}{2g}$
$Range,\ \ R = \frac{u^{2}sin2\theta}{g}$
$Given,\ \ H = \frac{R}{2}$
$\therefore\ \frac{u^{2}\sin^{2}\theta}{2g} = \frac{u^{2}2sin\theta cos\theta}{2g}$
$or\ \ sin\theta = 2cos\theta$
$or\ \ tan\theta = 2$
$or\ \ \theta = \tan^{- 1}(2)$