Dr. Cohn is testing how long it takes for a person's body to process a new medicine. She observes that the medicine is used by the body at a constant rate. For her latest test, Dr. Cohn starts with 15 milligrams of the medicine and notes that 12.6 milligrams remain unused after 1 hour. Which equation could Dr. Cohn use to solve for p, the percentage of the medicine that is used in 1 hour? A. p100=12.615 B. p100=2.415 C. p15=1002.4 D. p15=10012.6