When a pharmaceutical drug is injected into the bloodstream, its concentration at time t can be approximated by C(t) = Coe , where Co is the concentration at t= 0. Suppose the drug is ineffective C2 below a concentration C, and harmful above a concentration C2. Then it can be shown that the drug should be given at intervals of time T, where T= In A certain drug is harmful at a concentration three times the concentration below which it is ineffective. At noon an injection of the drug results in a concentration of 2 mg per liter of blood. Four hours later the concentration is down to 1 mg per liter. How often should the drug be given