$d = 5 \sin \left( \dfrac{2\pi}{13} \right)t + 9$

When *t* = 13/4

$d = 5 \sin \left[ \left( \dfrac{2\pi}{13} \right) \cdot \dfrac{13}{4} \right] + 9$
$d = 5 \sin \left( \dfrac{\pi}{2} \right) + 9$

$d = 14 ~ \text{m}$

When *t* = 39/4

$d = 5 \sin \left[ \left( \dfrac{2\pi}{13} \right) \cdot \dfrac{39}{4} \right] + 9$
$d = 5 \sin \left( \dfrac{3\pi}{2} \right) + 9$

$d = 4 ~ \text{m}$

The depth of the high tide is 14 meters and the depth of the low tide is 4 meters.

Answer = [ C ]