We consider that the 50% given in this item is by volume. Molarity is the unit of concentration that takes into account the number of moles of the solute and the number of moles of the substance.
number of moles of NaOH = (0.1 moles / L)(0.4 L) n = 0.04 moles of NaOH
If we are to take the basis of 1 mL of 50% NaOH solution,
(1 mL solution)(1.525 g/mL)(0.50) = 0.7625 g The number of moles is, 0.7625 g NaOH x (1 mol / 40 g) = 0.01906 moles of NaOH
volume of solution required = (0.04 moles of NaOH)(1 mL solution / 0.01906 moles of NaOH)