system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5- [physics?] firing a gun from a moving train.

So lets say I'm of the front of a train traveling 200mph (it's a special train that goes 200 mphs). And I firing me gun directly ahead of me. Does this add or subtract from the speed of the bullet? Also, if I was on the rear of the train and fired that direction would it have a different effect?
gpt
In relation to the train, bullet would go at the speed of a bullet. 

In relation to someone standing near the tracks, it would go at the speed of a bullet + speed of a train. 

If you were to shoot opposite to the direction of a train, your bullet would go at bullet speed - train speed.

If you were to shoot at an angle, you would have to do some trigonometry to calculate its speed and exact direction.

EDIT This is an approximation that works only on normal speeds. When you start adding speeds of light, then you need another equation because time and space do very weird things at these speeds.