Calculus related rates?

Question

Two cars are traveling along perpendicular roads, car A at 40 km/hr east, car B at 20 km/hr south. When car A reaches the point where their paths have an intersection, car B is 100 km north of the intersection. Find the rate at which the cars are separating from one another 2 hours later.
I got 20 km/hr, but this seems wrong. I did the entire set up; I didn't just subtract the numbers. Can someone check my answer please, and explain if I'm wrong?

Answer 1

Your answer is correct. Why does it seem wrong to you?

Did you get the answer of 20 from something that looked like this:

[(80)(40) + (60)(-20)]/100 = 20

?