The answer is 21.92g.
How I got this was plugging the molarity into the concentration formula on the reference tables.
Molarity = moles of solute/liter of solution
.75 = x/.5
.75 x .5 = .375 mol
You then plug the moles into the Mole Calculations formula on the reference tables. You need to find the gram-formula mass of sodium chloride, or NaCl. You add up the atomic masses of both and get 58.44277g.
Number of moles = given mass/gram-formula mass
.375 = x/58.44277
.375 x 58.44277 = 21.91603875 g
Round your answer to the nearest hundredth, and you get 21.92g! :)