a. Find the marginal revenue function if R(x)=31x-.04x^2

b. Find the marginal profit function if C(x)= 750+19x-.6x^2 and R(x)= 39x-.07x^2

c. The total cost (in dollars) of producing x coffee machines is C(x)=1800+60x-.2x^2 Find the exact cost of producing the 21st machine. and Use marginal cost to approximate the cost of producing the 21st machine. d. The total profit (in dollars) from the sale of x answering machines is. P(x)= 20x-.5x^2-290 Find the exact profit from the sale of the 26th machine. and Use the marginal profit to approximate the profit from the sale of the 26th machine. Thank you!