3 Molar solution means there are 3 moles of Na Cl salt in 1 Liter. Molecular weight of Na Cl = 58.44. Hence, there are 3 * 58.44 gms in 1 Litre of water.

Density = mass/volume

Mass of 1 litre of solution = 1.25 gms/ml * 1000 ml = 1, 250 gms

V = volume of water added to make the solution

175.32 gms + 1 gm /ml * V = 1, 250 gm

=> V = 1, 074.68 ml

So 1,074.68 ml or 1, 074.68 gms of water is mixed with 3 moles of NaCl to make the 3 M solution.

Molality = mass of solute in number of moles / mass of solvent in kg

= 3 / 1.07468 kg

= 2.7915 Molal