Final answer:
The depth of water at high tide is 11 feet.
Step-by-step explanation:
To find the height of the water at high tide, we need to find the maximum value of the function y = 4 sin (7x) + 7. The maximum value of a sine function is 1, so the maximum height of the water at high tide is 4(1) + 7 = 11 feet. Therefore, the depth of water at high tide is 11 feet.