Question

Two airplanes left an airport at the same time traveling in opposite directions. One travels at a speed of 190 miles per hour. The other travels 210 miles per hour. How long will it take for the planes to be 2000 miles apart?

Answer 1

190x + 210x = 2000
400x = 2000 <-- Combine like terms 

x = 5

In 5 hours they will separated by 2000 miles.

Answer 2

plane 1s speed function is a = 190t and 2 is b = -210t
lets times each by 10.
1900
-2100
1900-(-2100)
4000
now 5
950
-1050
950-(-1050) 2000
the answer would be 5 hours when they are at least 2000 mi apart