(c) $\mu = \frac{\sin\left( \frac{A + \delta_{m}}{2} \right)}{\sin\frac{A}{2}} \Rightarrow \sqrt{3} = \frac{\sin\left( \frac{60{^\circ} + \delta_{m}}{2} \right)}{\sin\frac{60{^\circ}}{2}}$
$\Rightarrow \frac{\sqrt{3}}{2} = \sin\left( 30{^\circ} + \frac{\delta_{m}}{2} \right) \Rightarrow \delta_{m} = 60{^\circ}$