The first answer should be correct if you used literal equations. You first start off with c = 8x + 5y. To make it easier, if you move the c= to the other side, you'd get 8x + 5y = c. Then, you subtract 8x on both sides leaving you with 5y = c - 8x. Last, you would divide c - 8x by 5, which leaves you with you final answer of y=(c-8x)/5