Related rates help: How fast is the distance between the ships changing at 5 pm?

[sisizheng]

At 1 pm, ship A is 120 km west of ship B. Ship A is sailing north at 20 km/h and ship B is sailing west at 15 km/h/ How fast is the distance between the ships changing at 5 pm?

 

[stapel]

At 1 pm, ship A is 120 km west of ship B. Ship A is sailing north at 20 km/h and ship B is sailing west at 15 km/h/ How fast is the distance between the ships changing at 5 pm?

What are your thoughts? What have you tried? How far have you gotten? Where are you stuck? For instance, you started by drawing the picture. You labelled a point "A" and, a bit to the right of this, another point "B". You labelled the distance between the points as "120". You draw a vertical line from A, labelling it with the given rate of change. You labelled the "120" line with the rate of change in that direction, too. You used what you learned back in algebra to create expressions for the lengths of the vertical and the horizontal lines. You applied the Pythagorean Theorem to the hypotenuse of the right triangle (being the distance between A and B). And... then what?

Please be complete. Thank you!