3- The student council normally sells 1500 school T-shirts for $12 each. This year they plan to decrease the price of the T-shirts. Based on student feedback, they know that for every $0.50 decrease in price, 20 more T-shirts will be sold. a) Determine the demand, or price, function. b) Determine the marginal revenue from the sales of 1800 T-shirts. c) The cost of producing x T-shirts is C(x) = -0.0005x + 7.5x + 200. Determine the marginal cost of producing 1800 T-shirts d) Determine the actual cost of producing the 1801st T-shirt. e) Determine the profit and marginal profit from the sale of 1800 T-shirts.