What’s the equation?

The CPM satellite (set up by students to beam solutions to problems around the world) follows an orbit in which it is over the northern hemisphere half of the time and the southern hemisphere the other half. You have been asked to help the observers on the ground locate the satellite by giving them a formula for the location at any time after the launch.    You know the following information:  The satellite’s greatest distance north of the equator is 4500 kilometers, which it reaches two hours after the launch. Six hours later, a bit more than half-way through its orbit, the satellite reaches its greatest distance south of the equator, which is also 4500 kilometers. The satellite takes twelve hours to complete an orbit. I need to find the equation and sketch the graph, but I don’t know how.