Making the simplistic assumption that the dissolved nacl(s) does not affect the volume
of the solvent water, determine the constants m and b in the equation molarity = m⋅density + b that relates the nacl molarity to the nacl(aq) density. take the density of water to be 1.00 g/ml and the molar mass of nacl to be 58.5 g/mol.

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if we assume volume NaCl + volume H2O = volume H2O.. i.e.. NaCl does not effect volume 

therefore.. the units of.. 
.. M = moles NaCl / L solution ≈ moles NaCl / L H2O 
.. density = grams NaCl / L solution ≈ grams NaCl / L H2O 
again.. that is our assumption 

so we can readily see that 
.. M = (1 mol NaCl / ___g NaCl) x (__g NaCl / L H2O) + 0 
ie.. 
.. M = (1 mol NaCl / 58.5g NaCl) x density solution + 0 

so.. we would expect.. 
.. m = 0.01709 mol / g 
.. b = 0