The Bay of Fundy in Canada has the largest tides in the world. The difference between low and high water levels is 20 meters. At a particular point the depth of the water, y meters, is given as a function of time, t, in hours since midnight by y = D + A cos(B(t ? C)).

a) What is the value of B? Assume the time between successive high tides is 12.7 hours. Give an exact answer.
b) What is the physical meaning of C?