A train goes forward at a speed of 1 m/s for 20 seconds. Then it stops
and goes backward at a speed of 0.5 m/s for 4 seconds. After both
movements are completed, how far is the train located from its
starting point? (I am asking for the train's final location, not the
total distance that it traveled)

Hi again traveler7!!

Divide the problem in two steps:

a-. the train goes forward at a speed of 1 m/s for 20 seconds.

In this case the traveled distance is:

Da = Va * Ta = 1 m/s * 20 s = 20 m  --> Forward.


b-. The train goes backward at a speed of 0.5 m/s for 4 seconds. 

Db = Vb * Tb = 0.5 m/s * 4 s = 2 m --> Backward 


Note that the speed in the second case is in the opposite direction,
then to find the total distance we must rest the backward distance
from the forward distance. The train moves forward 20 meters and then
it stops and moves back 2 meters:

Total Distance = Da + Db = 20 m - 2 m = 18 m 

At the end of both movements the train is located 18 m  from its
starting point in the forwards direction.


Regards.
livioflores-ga