7.0 g in 220 ml corresponds to 7 x 1000/220 = 31.818g per 1000 cc of solution or 1 liter of solution
Molarity is moles per liter of solution by definition, so we need to know the number of moles of NaCl in 31.818 grams. The molar mass of NaCl is 58.5 grams(rounded off), so # moles = 31.818/58.5 = 0.543. 0.543 moles in a liter of solution defines the concentration as 0.543M
