How to add a Score Multiplier and a Text show how much score gain

Unity Engine
1

i trying to get a scoremanager script working it work find but i want to add a score multiplier to every enemy when i kill the enemy and boss. and also text showing how much score i gain and fade out like this game

this is my scoremanager script

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class ScoreManager : MonoBehaviour {

    public static int score;

    Text text;
    void Awake ()
    {
        text = GetComponent<Text> ();

        score = 0;
    }
   
    // Update is called once per frame
    void Update (){
       

        text.text = "" +  score;
   
    }


}
2

I Have a Another Score script but i still want the multiplier

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class ScoreManager : MonoBehaviour {

    public static int score{ get; private set;}
    float lastEnemyKillTime;
    int streakCount;
    float streakExpiryTime = 1;
    public Text scoreUI;

    Text text;
    void Start ()
    {
       
        Health.EnemyDeath += OnEnemyKilled;
        PlayerHealth.PlayerDeath += OnPlayerDeath;
        text = GetComponent<Text> ();

        score = 0;
    }

    void OnEnemyKilled ()
        {
        if (Time.time < lastEnemyKillTime + streakExpiryTime) {
            streakCount++;
        } else {
            streakCount = 0;
        }

        lastEnemyKillTime = Time.time;
        score += 5  + (int)Mathf.Pow(5, streakCount);
        }


    void OnPlayerDeath ()
    {
        Health.EnemyDeath -= OnEnemyKilled;
    }
    // Update is called once per frame
    void Update (){
       
        scoreUI.text = score.ToString("D6");
        text.text = "" +  score;
   
    }


}