(b) $\frac{v^{2}\sin{2\theta}}{g} = \frac{\sqrt{3}v^{2}}{2g}$
or $\sin{2\theta} = \frac{\sqrt{3}}{2}$ or $2\theta = 60{^\circ}$ or$\ \theta = 30{^\circ}$
Let us cross-check with the help of data for vertical range
$\frac{v^{2}\sin^{2}\theta}{2g} = \frac{v^{2}}{8g}\ \ \ or\ \ \ \sin^{2}{\theta = \frac{1}{4}}$
$or\ \ sin\ \theta = \frac{1}{2}\ \ \ or\ \ \ \theta = 30{^\circ}$