A total-revenue function is given by R(z) = 1300 2-0.42 where R(z) is the total revenue, in thousands of dollars, from the sale of an airplanes. Find the rate at which the total revenue is changing when 30 airplanes have been sold. dollars per airplane Round to two decimal places. A total-cost function is given by C(a)=1100(+5)/3 +600 where C(a) is the total cost, in thousands of dollars, for the production of airplanes. Find the rate at which the total cost is changing when 21 airplanes have been sold. dollars per airplane Round to two decimal places.