"I thought that I read something somewhere that said that marginal cost is equal to price."

I think the book says that Marginal Cost = supply price in a short-run competitive market.  Thus in order to maximize profit the price must equal marginal cost.  In parts B and C I got a shutdown price of $5 occuring at a quantity of 5.  The table says that at a quantity of 5, var_cost=25 and fix_cost=10 for a total cost of 35.  Part C says that at the shutdown price, the total revenue = total variable cost (which is 25 on the according to the table).