The vertical displacement

y of a boat that is rocking up and down on a lake. y was measured relative to the bottom of the lake. It has a maximum displacement of 12 meters and a minimum of 8 meters, a period of 3 seconds, and an initial displacement of 11 meters when measurement was first started (i.e., t = 0). assume at t = 0 function is increasing. ---> full period = 6 secs therefore, b = 2 pi / 6 = pi/3 Amplitude = 2 D = 10 I'm just getting confused with the initial displacement of 11 m. Anyone please help me out