#### Answer

$\lim\limits_{t \to 12^-}f(t)=150$
$\lim\limits_{t \to 12^+}f(t)=300$
The $150$ difference between the right and left hand limits is consistent at $4, 8, 12, 16$ hours. This shows that the amount $f(t)$ of the drug in the bloodstream is suddenly increased by $150$ every $4$ hours reflecting the fact that the patient receives a $150$ mg injection of the drug every $4$ hours.

#### Work Step by Step

One-sided limits can be found by observing both sides of $f(t)$ as $t$ approaches a certain value.