how can i do to generate floor

i do this script but he doesn’t work , he genrate floor in the same place
how can i do , pleaaase help me

using UnityEngine;
using System.Collections;

public class GenerateFloor : MonoBehaviour {
    
    GameObject Floor;
    GameObject InstanceFloor;
 
    public GameObject obstacle;
    float x;
   


    void Awake()
    {
        Floor = GameObject.FindGameObjectWithTag("floor");
        obstacle = GameObject.FindGameObjectWithTag("plane");
        
    }

    void OnCollisionEnter(Collision col)
    {
        if (col.gameObject.tag == "plane")
        {

             x = Floor.transform.position.x - 100;

             

             InstanceFloor = (GameObject)Instantiate(Floor, new Vector3(x, 4.2f, -11.6f), Quaternion.identity);
          
            
           
             
        }

    }
   
	// Use this for initialization
	void Start () {
       
	}
	
	// Update is called once per frame
	void Update () {
        
    }
}

Line 26:

x = Floor.transform.position.x -= 100;

You forgot an = sign.