a. He will have 32 mg 5.7 hours after 8:00 am or at approximately 1:45.
He will have \(64(.5)^\frac{4}{5.7} ≈ 39.3\); \(39.3\) mg left at noon.
He will have \(64(.5)^\frac{12}{5.7}≈14.9\); \(14.9\) mg left at 8 pm.
He will have \(64(.5)^\frac{18}{5.7}≈7.2\); \(7.2\)mg left at 2 am.
b. Equation \(A = 64(.5)^\frac{t}{5.7}\)