To find the mass of a solute in a given mass of solution, you use the mass percent (or percent by mass) of the solute.Formula: Mass of solute = [(Mass % of solute)/100]*(Mass of solution)Example:200g of a salt solution that is 10% by mass salt: Mass Salt = [(10%)/100]*(200g) Mass Salt = [(0.10)]*(200g)Mass Salt = 20 grams