Answer:
The interval of decrease is 0 ≤ x ≤ 1.25
Explanation:
First, we have to find the point where it changes from increasing to decreasing or decreasing to increasing.
The graph shows that there is a decrease before 1.25 h, and it increases after 1.25 h also.
We can further prove that 1.25 is the point of change when we enter 1.25 in place of t in the given equation
d(1.25) = 40|1.25 - 1.25| = 0
We see that the graph is decreasing before 1.25, so the interval will have to end at 1.25.
We also see that there is no increase before 1.25, so we can make the interval begin at 0