English is not my first language and i don't seem to understand what it is asking or how the diagram should look. Can someone help me interpret and give me some advice?

At noon, ship A passes the point P that is 8 km west of a harbour, heading due north at 8 km/h. At 10 a.m., ship B had left the harbour, sailing due north at 6 km/h.

Give an expression for D, the distance between the two ships, in terms of t, the number of hours after noon.