The density of 3M solution of NaCl is 1.25 g/mL. Calculate molality of the solution

The density of 3M solution of NaCl is 1.25 g/mL. Calculate molality of the solution

Given:
Density of solution = 1.25 g/mL
M =3 mol/lit
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Molality of the solution is 2.79 m.