Answer
$V(t) = 2250+250~sin(\frac{\pi~t}{2})$
Work Step by Step
The average volume is 2250 mL.
The amplitude of the graph is 250 mL.
The period is 4 seconds.
We can use these values to write a function that models the depth:
$V(t) = 2250+250~sin[\frac{2\pi}{4}~t]$
$V(t) = 2250+250~sin(\frac{\pi~t}{2})$
