Need help on the explanation

You are captain of a submarine and your first mate has just detected an enemy destroyer in the area at time t = 0. As an evasive maneuver you have decided to porpoise (go shallow, then deep, and so on) the submarine. At t = 4 minutes, you are at the deepest point, -1000 meters. At time, t = 9 minutes, you reach your shallowest point, at -20 meters. If you assume your submarine depth varies sinusoidally with time, complete the following: a) Sketch the graph of the depth of the submarine versus b) Write an equation that would express the depth of th. time . submarine versus time c) Your submarine is safe when it is below -350 meters. d) Find the first time after 0 minutes when your sub Was your sub safe at time + = 0? Justify your response. becomes safe