The revenue equation in hundreds of millions of dollars) for barley production in a certain country is approximated by R(x) = 0.0671x2 +1.2933x + 2.0269 where x is in hundreds of millions of bushels. Find the marginal-revenue equation and use it to find the marginal revenue for the production of the given number of bushels. (a) The marginal-revenue equation is R'(x) =. (Round to four decimal places as needed.) (b) Find the marginal revenue for the production of 500,000,000 bushels. The marginal revenue is hundred million dollars. (Type an integer or decimal rounded to two decimal places as needed.) (c) Find the marginal revenue for the production of 550,000,000 bushels. The marginal revenue is hundred million dollars. (Type an integer or decimal rounded to two decimal places as needed.)