Molality = moles of solute/mass (in kg) of solvent
The solute here is NaCl, of which you have 40 g or 40/58.4428 = 0.6844 moles NaCl.
The solvent here is water, of which you have 1500 g or 1.500 kg H2O.
The molality of the resulting solution would thus be 0.6844 moles NaCl/1.500 kg H2O = 0.4562 mol/kg.
If you have to consider sig figs, then your final answer would have one sig fig (40 g has one sig fig). In that case, your final answer would be 0.5 mol/kg.
