Answer
a. $0\lt t \lt 3$
b. The derivative is decreasing an hour before.
Work Step by Step
a. From what can be seen on the graph, the function appears to be sloping upwards from the time $t=0$ to $t=3$ indicating that the effectiveness of the medicinal drug is increasing with time.
b. The drug reaches a maximum when the function has a peak, which takes place at $t=3$. This is when the effectiveness is maximized. Drawing a tangent line would give us a horizontal line where the derivative will be equal to 0.
As the time increases an hour before the 3 hour mark, the derivative appears to be diminishing. While the derivative from $t=2$ to $t=3$ is positive, it appears that the drug is becoming more effective more and more slowly, indicating that the value of the derivative itself is decreasing. ( Second derivative is negative )
