The mass, M, of ibuprofen in the bloodstream is given by the

equation M=(0.69)', where I is the initial dose and t is the number

of hours since the dose. Suppose a patient is given an initial dose

of 200 mg. When will the amount of ibuprofen in the bloodstream

be reduced by a factor of one-half? Round your answer to the

nearest tenth of an hour. [5 marks]