Use the fact that the amount of a drug in a patient at time t is given by D(t)=…

Use the fact that the amount of a drug in a patient at time tt is given by D(t)=D0eln(12)tD\left(t\right)=D_0e^{-\ln\left(12\right)t} mg with the initial dose of the drug being 60 mg. The next dosage of the drug cannot be administered until there is only 5 mg of the drug left in the patient's body. After how long, in hours, should the patient wait to take the next dose?
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