The total revenue (in hundreds of dollars) from the sale of x spas and y solar heaters is approximate by R(x,y) = 10+ 190x + 188y -5x2-7y- 3xy. Find the number of each that should be sold to produce maximum revenue. Find the maximum revenue. . . .. . Find the derivatives Rxx, Ryy, and Rxy- Rxx= Ryy = Rxy Selling spas and solar heaters gives the maximum revenue of $. (Simplify your answers.)