Step-by-step explanation:
step 1. sinbt cycles twice a day throughout 2pi where t is 0 to 24 hours so b = pi/6
step 2. tide varies between 24m and 12m thus having a medium of (24 + 12)/2 = 18m and a magnitude of 6m
step 3. d = 18m and a = 6m.
step 4. looks like the first option.
