How to kill enemy when the bullet hits the BoxColllider2D?

Hello! I´m currently working in a game and I´m having trouble here. My enemy has two colliders (BoxCollider2D and CircleCollider2D). I use the CircleCollider2D to trigger the enemy (if the player is inside of the CircleCollider2D, the enemy will attack him). I knew that if my player shoots, bullet will collide with the CircleCollider2D first. I´m having trouble cause I only want to apply damage when the bullet hits the BoxCollider2D. Can you help me solve this?

Here´s my code:

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

public class Bullet : MonoBehaviour {

 public float vel = 5f;

 Rigidbody2D rb;
 BoxCollider2D enemyhit;

 // Use this for initialization
 void Start () {
     rb = GetComponent<Rigidbody2D>();
 }
 
 // Update is called once per frame
 void Update () {
     print ("oribullet:" + transform.rotation.z);
     if (transform.rotation.z !=-1){
         rb.AddForce (Vector2.right * vel);    
     }else{
         rb.AddForce (-Vector2.right * vel);    
     }



     }

 void OnTriggerEnter2D(Collider2D other)
 {
     if (other.gameObject.tag == "bomber") 
     {    
             DestroyObject (other.gameObject);
             Destroy (gameObject);
     }
 }

}