I can't get Text Mesh to disappear in the scene / How do I make the Text Mesh disappear in my scene

I only can get the Text Mesh to appear in the scene . The thing is I want the text to appear in scene five seconds later and disappear eight seconds later . I don't have any errors . I don't know why it's not working here is my script :

  using UnityEngine;
    using System.Collections;
    using UnityEngine.UI;
    
    public class oik : MonoBehaviour {
    
     private Text text;
  
       public float timeShown;
    
    
         void ShowMessage(string message, float timeToShow = 10)
     {
         StartCoroutine(ShowMessageCoroutine(message, timeToShow));
     }
        
         IEnumerator ShowMessageCoroutine(string message, float timeToShow = 10)
     {
  
         while (timeShown < timeToShow)
         {
             timeShown += Time.deltaTime;
             yield return null;
         }
  
         text.text = " The Reqiure Score is 1700" ;
     }
    }