9 An accessories company finds that the revenue, in dollars, from the sale of x belts is given by R(x) = 35x . Find the rate at which average revenue is changing when 177 belts have been produced and sold. First, find the rate at which the average revenue is changing when x belts have been produced. R'(X) = When 177 belts have been produced and sold, the average revenue is changing at for each additional belt. (Round to four decimal places as needed.)