Step 1 :We are given the equation \(y=390(0.85)^{t}\) which models the amount of medicine in a patient's bloodstream t hours after taking a pill.
Step 2 :We need to find the time t when the amount of medicine y in the patient's bloodstream reaches 150 milligrams.
Step 3 :This can be done by setting \(y=150\) in the given equation and solving for \(t\).
Step 4 :Substituting \(y=150\) into the equation, we get \(150=390(0.85)^{t}\).
Step 5 :Solving this equation for \(t\), we get \(t=5.88\).
Step 6 :Final Answer: The patient needs to take the second pill approximately \(\boxed{5.88}\) hours after taking the first pill.