Related rates change in distance between two boats?

[unigirl123101]

Homework Statement

Two boats leave a dock at the same tie. One goes south at 30 km/h and the other goes southwest at 40 km/h. What is the rate of change of the distance between the 2 boats, 30 minutes after they leave?

I know how to do these questions when it's a right triangle...but since this has one boat going south, and one going southwest...I don't know how to do it.

 

[hotvette]

I think you can make 2 right triangles by drawing a line from the position of first boat perpendicular to the path of the 2nd boat. Also, don't you know the angle between the paths of the two boats?