5. Painful bone metastases are common in some advanced cancers. Physicians often order treatment with Strontium-89 (Sr-89), a radionuclide with a strong affinity for bone tissue. A patient is given a sample containing 4 mci (millicuries) of Sr-89. After 90 days, 20% of the original amount of Sr-89 remains in the body. a) Write a function of the form Q(t) = Qo e to model the amount Q(t) of radioactivity in the body t days after the initial dose. a) What is the biological half-life of Sr-89 in this treatment? (Round answer to the nearest tenth of a day.)