A Hospital Patient Receives 4 Units of a Certain Drug $f ( t ) = e ^ { - t / 12 }$

Multiple Choice

A hospital patient receives 4 units of a certain drug per hour intravenously. The drug is eliminated exponentially, so that the fraction that remains in the patients body for t hours is $f ( t ) = e ^ { - t / 12 }$ . If treatment is continued indefinitely, approximately how many units of the drug will be in the patient's body in the long run?

A) 44 units
B) 48 units
C) 52 units
D) 56 units