Carlos has taken an initial dose of a prescription medication. The relationship between the elapsed time t, in hours, since he took the first dose, and the amount of
medication, M(t), in milligrams (mg), in his bloodstream is modeled by the following function.
M(t) = 20 -e-0.8t
In how many hours will Carlos have 1 mg of medication remaining in his bloodstream?
Round your answer, if necessary, to the nearest hundredth.
hours