(b)
$\mathrm{\Delta}T_{b} = mk_{b}$
$\ \ \ \ \ \ \ \ \ \ \ \mathrm{\Delta}T_{f} = mk_{f}\$
$\frac{\mathrm{\Delta}T_{b}}{\mathrm{\Delta}T_{f}} = \frac{k_{b}}{k_{f}} = \frac{0.512}{1.86}$
$\mathrm{\Delta}T_{b} = \frac{0.512}{1.86} \times 0.186$
=0.0512${^\circ}$