How to increase the speed of the background as time goes on (unity 2d),How to increase the speed as time goes on (unity 2d)

So I want the speed of the background to increase as time goes on. For example, every 20 seconds the speed is increased by 20%. I can't figure out how to do this and any help would be appreciated. Here's my script :).

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class FloorScroller : MonoBehaviour { public BoxCollider2D collider; public Rigidbody2D rb;

 private float width;

 private float scrollSpeed = -7.5f;



 // Start is called before the first frame update
 void Start()
 {
     collider = GetComponent<BoxCollider2D>();
     rb = GetComponent<Rigidbody2D>();

     width = collider.size.x;

     rb.velocity = new Vector2(scrollSpeed, 0);
 }

 // Update is called once per frame
 void Update()
 {
     if(transform.position.x < -width)
     {
         Vector2 resetPosition = new Vector2(width * 2f, 0);
         transform.position = (Vector2)transform.position + resetPosition;

     }

 }

}