The general formula for mass percent of a solution is:
% m/m = [grams of solute] / [grams of solution] * 100
And grams of solution = grams of solute + grams of solvent.
So, in our problem:
Solute = NaCl => mass of solute = 59.56 g
Solvent = H2O => mass of solvent = 165.1 g
=> mass of solution = 59.56 g + 165.1 g = 224.66 g
=> % m/m = [59.56 / 224.66] * 100 = 26.51 g (using four significant figures).
Answer: 26.51%
