Chapter 1.5, Problem 10E

A patient receives a 150-mg injection of a drug every 4 hours. The graph shows the amount $f\left(t\right)$ of the drug in the bloodstream after t hours. Find

$\underset{t\to {12}^{-}}{\lim }f\left(t\right)$ and $\underset{t\to {12}^{+}}{\lim }f\left(t\right)$

and explain the significance of these one-sided limits.