The concentration of a certain drug in a patient's bloodstream, D, in milligrams, can be modeled by the function D(x) =-x* + 5x3 - 10x2 + 50x, where x is the amount of the time, in hours, since the drug was administered.
Ignoring imaginary or complex values for x, after how many hours would it take for no drug to remain in the bloodstream?