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A research lab has a 12 mg sample of a radioactive substance. The amount of the substance, A(!), in milligrams, left in the sample can be modeled by the half-life function 8 5 A(t) = 12 where / represents the time, in days, after the initial time. How long does it take for the sample to reduce to 3 mg? *(The exponent is t / 8.5)