1.6g in 1.0L for a 0.04 Molar solution, 1.6g in 1.0kg solvent (water) for a 0.04 molal solution, or 0.4g in 1.0 kg (total mass) for 0.04% wt/wt solution.
Normally, such solutions are either volume/volume (Molar) or mole/weight (molal). You did not specify which. It may be a simple weight percentage as well.
A 0.04 molal solution is 0.04 moles per 1kg solvent, which does not include the solute. Thus a 0.04 molal solution would be made by taking 1.6g NaOH and dissolving it in 1kg water. NOTE that this will result in a final solution volume slightly greater than 1L, which is the difference from the following Molarity calculation.
A 0.04 Molar solution is 0.04 moles of NaOH in enough water to make a 1.0L final total solution. The mass of NaOH needed to make the solution is 0.04 moles * 40g/mol NaOH = 1.6g.
You can make a full liter of it, or reduce the amount to make just what you need. 0.15L/L * 1.6 = 0.24g NaOH in 150mL water.