The concentration of a drug (in parts per million) in a patient's bloodstream thours after administration of the drug is given by the function P() = - 4 + 6 3 - 31 2 + 66. The corresponding graph is shown to the right. Complete parts a through .
Use the formula to determine when the drug will be totally eliminated from the bloodstream. The drug will be totally eliminated from the bloodstream in ____ hours.
(Simplify your answer.)