please solve in simple way .

and please use the notes

9. The cost function for the manufacture of x number of goods by a company is C(x) = xVx3 - 10x2 + 9000. The revenue is given by R(x) = Ax xe$x*-1 (Note: A is 7) a. Find the level of output at which the cost is minimum, then find the minimum cost. b. Find the marginal Revenue