A Patient Is Given an Injection of 21 Units of a Certain

Multiple Choice

A patient is given an injection of 21 units of a certain drug every 24 hours.The drug is eliminated exponentially so that the fraction that remains in the patient's body after t days is $f ( t ) = e ^ { - t / 5 }$ If the treatment is continued indefinitely,approximately how many units of the drug will eventually be in the patient's body just prior to an injection?

A) 94.85 units
B) 46.65 units
C) 115.85 units
D) 141.50 units