No such thing as a vertex of a graph... Eliminate B and C. Try f(3) = 4(3-5)(3+3) is not zero eliminate A. So answer must be D. Check: f(-3) has factor -3+3 = 0. f(5) has factor 5-5 = 0.
The following formula is used to find the answer. D = 50 mg (0.6^n) D is the dosage n is at any hour Using this formula and solving the equation for it, the answer is 18.
