Two cars start moving from the same point. one travels south at 60 mi/h and the other travels west at 25 mi/h. at what rate is the distance between the cars increasing four hours later?

Oops, I missed they we're moving perpendicularly. Gotta be more careful.  I'm gonna blame this immovable answer box popping up and hiding the question on my browser. Plus I skimmed it.

We wont worry about the signs; they won't matter.  We have car 1  (x,y)=(0,60t) and car 2 (x,y)=(25t,0).  So the squared distance is

recognizing the Pythagorean Triple.  Everything's positive so

So they're moving apart at a constant 65 mph.

65 mph

you can first factor out the n to get n(1+5). we know that 1+5 is 6, so we just have 6n.