the code fiixing the size camera and the background

Hi everyone I'm learning unity and i find the code for fix the size background foreach device you running the game but i try to understand the calculation in the code so i need some help to understand the calculation code and thanks

The code : using UnityEngine; using System.Collections;

 public class BGscript : MonoBehaviour {
 
     
     void Start () {
     SpriteRenderer sr = GetComponent<SpriteRenderer>();
     Vector3 tempScale = transform.localScale;
     float width = sr.sprite.bounds.size.x;
 
     float WorldHeight = Camera.main.orthographicSize * 2.0f;//why multiply the camera *2.0f
     float WorldWidth = WorldHeight/ Screen.height * Screen.width;
 
     tempScale.x = WorldWidth / width;
 
     transform.localScale = tempScale;
     }
 
 }