as the tides change,the water level in a bay varies sinusoid

as the tides change,the water level in a bay varies sinusoidally.at high tide today,at 8am,the water level was 15feet; at low tide,6hours later at 2pm,it was 3 feet.how fast,in feet per hour,was the level dropping at noon today
A 3 B pai(3)^(1/2)/2 C 3(3)^(1/2) D pai*(3)^(1/2) E 6(3)^(1/2)