The minimum depth,dft of water in a harbourthours after midnight can be approximated by the function:d(t) = 35 + 15cos0.5t

0<=t<= 24

a) A ship with a draught of 25ft is in harbour at midnight. By what time must it leave to prevent grounding?

b) What is the next time it can return to harbour?

Answers: a) 04:36 b) 10:53

how do you do this? Thanks.