How do I check if X position is increased by 5?

I want to make a prefab do something when after its X position has been increased to 5.

Does anyone know how I can check if the X position of a prefab is increased by 5.

I am using C#. Any clue as of how I can do this would be greatly apreciated.

Here is some pseudo code.

private Vector3 startPos;

void Start()
    startPos = transform.position;

void Update
    if (transform.position.x + 5 >= startlocation.x)