| a= 60 mph North
L__________> b= 25 mph East
If you're going to look at the figure above, the rate that we are looking for is the hypotenuse of a right triangle. From 8am to 10am is 2 hours.
So let say:
c = rate of the distance between the car is changing.
Using the Pythagorean Theorem.
c2 = a2+b2
c2 = (60)2+(25)2
c = 65 miles per hour.
The 2 hours doesn't matter because the rate is still going to be the same in any time. However, if you are looking for the distance after 2 hours, that would be (65)(2) = 130 miles.
65 miles per hour is basically the same as 130 miles in 2 hours.