The marketing department of a company has determined that if it spends x thousands of dollars on radio advertisements and y thousand dollars on newspaper advertisements, the company's revenue (in thousands of dollars) will be R ( x , y ) = − 0.06 x 2 − 150 y 2 + 2 x + 2 y + 4 x y How much money should this company spend on radio advertisements and newspaper advertisements to maximize its revenue?