The answer is D. 20%,
Because when you mix two substances together, the mass still remains the same, because according to the law of conservation of matter, you can’t destroy or create mass. So the total mass of the solution is 40g because 32g+8g=40g.
Since you’re looking for the percentage of the solute in the solution, you’re going to divide 8/40, and get a simplified fraction of 1/5, which equals 0.2. So, 20% :)