Are you referring to this part?
"Calculate the Ksp of KCl at 60o C if the density of the solution is 1.2 g/mL"
Pure water solvent has a density at 60o C of 1.0 g/mL. Therefore the extra 0.2 g/mL is the mass of the solute KCl.
Convert that extra 0.2 g into moles of KCl solute.
Convert the solute ions to concentrations in moles/L.
Then write the expression for the Ksp, substitute the values, et voila.
Does that answer your question?