By using the averages of high and low tide levels. The depth of the water in a seaport can be approximated by the sinusoid d=3.2sin0.166pi(t-2.5)+14.1 where d is the depth and t is the hours after midnight. if a ship needs at least 12 m of water in a seaport to dock safely, how long could the ship dock safely for? What I have tried so far... My attempt at this problem is to find the two points where the wave intersects y=12 and subtract the two points. 12=3.2sin0.166pi(t-2.5)+14.1 t=2.5+(asin((12-14.1)/3.2)/(0.166pi))=1.12 second solution is pi-1.12=2.02 subtracting the two gives me 0.90 hours which is incorrect the answer is 8.769 hours. Any ideas what I am doing wrong here?