3.0 molal NaOH solution has density of 1.110 g/ml.  The molarity of the solution is ----M

3molal means 3moles of solute per Kg of solvent(water)

Weight of solute = 3 x Molecular wt. = 3 x 40 = 120 g

Total weight of solution = 1000+120 = 1120g

$\mathrm{Volume} \mathrm{of} \mathrm{solution} = \frac{\mathrm{mass}}{\mathrm{density}}=\frac{1120}{1.110}$

$\mathrm{Molarity} =\frac{\mathrm{n}\times 1000}{\mathrm{V}}=\frac{3\times 1000\times 1.110}{1120}=2.9732$M