Answer:
4 seconds
D is correct
Explanation:
The height, h, in feet of a buoy in relation to sea level as a function of time, t, in seconds can be modeled by the graph attached.
We need to find the time when a buoy moves from highest point to lowest and than lowest to highest.
It means we have to find the time take between two consecutive highest point.
We will draw vertical lines at two consecutive highest point and mark time of that line.
Now we will take the difference of time.
This time will take to move a buoy highest point to its lowest point and then back to its highest point.
Please see that attachment for vertical line.
First Highest point H1 at t=1 seconds
Second Highest point H2 at t=5 seconds
Time take between H1 and H2 = 5-1 = 4 seconds
Hence, 4 seconds will take for buoy to go from its highest point to it's lowest point and then back to its highest point.