Now we know we want to create a 5% bimass solution of sodium chloride, so we use the formula 5% is equal to the number of sodium chloride we need to add in terms of grams divided by the total number of grams. So 180 grams of water that we already have, plus the x. The x is the number of sodium chloride in grams that we need to add multiply the whole thing by 100. This is simply the formula for mass percentage. Next we do a little algebra. We bring the 100 over.