An accessories company finds that the cost and revenue, in dollars, of producing x belts is given by 9 10 C(x) = 750+36x -0.067x and R(x) = 25x , respectively. Determine the rate at which the accessories company's average profit per belt is changing when 174 belts have been produced and sold. First, find the rate at which the average profit is changing when x belts have been produced. P'(x)=\