The enthalpy of solution of sodium chloride is $4\mathrm{kJ}{\mathrm{mol}}^{-1}$ and its enthalpy of hydration of ions is $-784kJ{\mathrm{mol}}^{-1}$ Then the lattice enthalpy of $\mathrm{NaCl}\text{ (in }\mathrm{kJ}{\mathrm{mol}}^{-1}\text{ ) }$, is