How to make UI text appear on screen for a limited time then disappear

If you've played Skyrim or a similar game, when you pick up a bag of gold it will come up on screen saying how much gold was in said bag, I am trying to achieve this.

Basically when the player presses E when the raycast is looking at the bag it will give the player a random amount of gold, my problem is I can't get the text that says "you collected 'x' amount of gold" to disappear from the screen after a few seconds, I have tried using coroutines but I don't fully understand them despite watching Unity videos on it and looking at the docs.

Any help would be greatly appreciated, I think once I understand coroutines better I will realise that I've made some stupid mistake or completely misunderstood the concept of coroutines. I am still quite new to unity so don't flame me please :)

here is what I have so far:

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 namespace UnityStandardAssets.Characters.FirstPerson
 {
     public class GoldBagController : MonoBehaviour, InteractableObject
     {
         public GameObject goldBag;
         public PlayerController player;
         public CharUI charUI;
         public float bagAmount;
         public bool isGoldCollected;
 
         void Start()
         {
             isGoldCollected = false;
             player.goldCount = 0;
             //charUI.goldAmount.text = "You got " + (int)bagAmount + " gold!";
         }
 
         void Update()
         {
             bagAmount = Random.Range(20f, 5000f);
         }
 
 
         IEnumerator GoldAmountTip(string message, float delay)
         {
 
             if (isGoldCollected == true) //when gold bag is collected add the gold to gold amount, remove the gold bag and print a message
             {
                 player.goldCount += (int)bagAmount;
                 charUI.hoverTip.text = "";
                 Destroy(goldBag);
                 charUI.goldAmount.text = message;
             }
 
             yield return new WaitForSeconds(delay); //delay for 3 seconds then set text to nothing, this is where I am having trouble
             charUI.goldAmount.text = "";
         }
 
         /**
          * Interact method is called when player presses E when its raycast is looking at the gold bag
          **/
         public void Interact()
         {
             isGoldCollected = true; 
 
             StartCoroutine(GoldAmountTip("You got " + (int)bagAmount + " gold!", 3));
         }
     }
 }