At 2:00 p.m. Ship A is 20 km west of a lighthouse and sailing due south at 18 km/h. At 2:30 p.m. Ship B is 15 km north of the lighthouse and begins sailing due east at 24 km/h. How fast is the distance between the two ships changing at 3:00 p.m.?
a) 30.0 km/h
b) ≈29.6 km/h
c) 27.9 km/h
d) 22.2 km/h