Question

At noon, ship A is 180 km west of ship B. Ship A is sailing east at 40 km/h and ship B is sailing north at 35 km/h. How fast is the distance between the ships changing at 4:00 PM? Answer in Km/h

Answer 1

You'll be expressing x's and y's parametrically in terms of time (t) and setting up a distance formula where D will ultimately be in terms of "t". Take the derivative of D in terms of "t" and then you can get rate of change at t=4.

Answer 2

You want rate of change ds/dt for the distance between the ships expressed as a function of t.