HW Q9I need help on my homework

Find the point of diminishing returns (x,y) for the function R(x), where R(x) represents revenue (in thousands of dollars) and x represents the amount spent on advertising (in thousands of dollars). R (x ) = (-x + 63x2 + 1250x - 500), 0sxs 25 The point of diminishing returns is (Type an ordered pair. Round to the nearest tenth as needed.)