Waves with an amplitude of 2ft pass a doc every 30 seconds. write an equation for a cosine model the height of a water particle above and below the mean water line

with that template in mind, let's see.

now, since the period is 30, and cos(x) starts off at 1, recall cos(0) = 1, so then le'ts move the starting point over by simply doing a horizontal shift to the right by a quarter of the period, 30/4 = 15/2 units, that way the initial "hump" starts off at 0.

Check the picture below.

answer: x=60