Solubilities of the compounds, $Ca(OH{)}_2$ and NaCl, at different temperatures are given below:

$\backslash$table$[[\frac{\frac{t}{}C}{Ca(OH{)}_2},NaC{l}_{?},],[60,0\mathrm{.}083,37\mathrm{.}05],[80,0\mathrm{.}066,38\mathrm{.}05]]$

$($a$)$ Calculate the heat of solution for the two systems.

$($b$)$ Interpret the calculated values of the heat of the solutions.