A drug's effectiveness decreases over time. If each hour,a drugis only 90% as effective as during the previous hour, at some point the patient will not be receiving enough medication and will need another dose. This can be modeled by the exponential function. In this equationis the amount of the initial dose, andyis the amount of the medication still available "t" hours after the drug was administered. Suppose the initial dose was300 mg. How long will it take for this initial dose to reach the dangerously low level of75 mg? Solve this problem algebraically, not with a graph or by plugging and checking.