Acompany expects that the number N(x) of a product sold during a week is related to the amount spent on advertising by the function N(x) = 5x3 + 180x2 + 1215x + 18,000, where x (with 0 5x527) is the amount spent on advertising in thousands of dollars. What is the point of diminishing returns? The point ofdiminishing returns is . (Simplify your answer. Type an ordered pair. Do not use commas in the individual coordinates.)