View difference between Paste ID: xUZ4SL0e and PdMkmzS6

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class BulletScript : MonoBehaviour
 {
     public float speed = 5f;
     void Start()
     {
         //delete the bullet after 3 seconds
         Destroy(gameObject,3);
     }
 
     // Update is called once per frame
     void Update()
     {
         //bullet movement
         Move();
     }
 
     void Move()
     {
         //moving up with the specified speed
         transform.position += Vector3.up * speed * Time.deltaTime;
     }
 
     private void OnTriggerEnter2D(Collider2D collision)
     {
         //If we touch an element with Alien tag
         if (collision.gameObject.tag == "Alien")
         {
             //Destroy that object
             Destroy(collision.gameObject);
             //and yourself
             Destroy(gameObject);
         }
     }
 }