Answer is: mass of KCl is contained in this solution is 80 grams.
m(solution) = 400 g.
ω(KCl) = 20% ÷ 100% = 0,2.
m(KCl) = m(solution) · ω(KCl).
m(KCl) = 400 g · 0,2.
m(KCl) = 80 g.
ω is the mass percent and it is expressed as the grams of solute (in this example potassium chloride) divided by the grams of solution, then multiplied by 100 to get percentage.