A drug is administered to a patient at the same time every day. Suppose the concentration of the drug is Cn (measured in mg/mL) after the injection on the nth day. Before the injection the next day, only 30% of the drug present on the preceding day remains in the bloodstream. Suppose the daily dose raises the concentration by 0.2 mg/mL.

a) Find the concentration after 3 days

b) Write a difference equation that expresses Cn+1 in terms of Cn

c) Find a formula for Cn as a function of n

d) Find the limiting value of the concentration