I can not understand how to do problem 21-1 in my accounting class. Bools is Accounting text and cases. The beta division of Gatham Industries.

I can not understand how to do problem 21-1 in my accounting class. Bools is Accounting text and cases. The beta division of Gatham Industries. Q. Determine the gross margin mix, selling price, and sales volume variacnes. Calculate the net gross margin variance directly, then as a check see if it equals the sum of the three variance components you calculated individually.