A mixture of copper(II) sulfate pentahydrate (249.70 g/mol) and magnesium sulfate heptahydrate (246.49 g/mol) is heated until all the water is lost. The weight of the initial mixture is 5.020 g, and the weight of the resulting anydrous compounds is 2.988 g. Which choice is closest to the percent by mass of copper(II) sulfate pentahydrate in the original mixture? Steps?