Gunther needs a 75% concentrated solution. When making his solution at room temperature, he could only make a solution that was 70% before the solute settled out.

What could he do to make his solution reach 75%?

Put the solution in an ice bath, dissolve the solute, and let it return to room temperature.

Heat the solution, dissolve the solute, and let it cool verifying nothing settled out.

Add more water, boil the solution, and dissolve the solute until the some of the water evaporates.

Keep the solution at room temperature, add more water, and dissolve the excess solute.