4. A group of patients is given a certain dose of a drug once. Two measurements of concentration of the drug in the blood are taken 24 hours apart to determine the concentration of the drug in the blood at time t. The measurements are given below. 1.5 0.2 0.6 (a) Write a DTDS of the form n+1 = rm: for drug concentration of the drug in the blood and nd (b) For patient 1, how long will it take until the drug concentration is below 0.1? :1 (c) How long does it take for the initial concentration to decrease by %50