Given:
Mass of solute(NaCl) = 40g
Mass of solvent(water) = 100ml = 100g
Mass of solution = 40+100 = 140g
Concentration of the solution in terms of mass percentage is given as,
Concentration of solution = Mass of solute/Mass of solution×100
40/140×100= 28.57%
Hence the Concentration of solution = 28.57%