Urgent help for Unity Game with deadline tomorrow

I am trying to make my tank shells do damage to these zombies, but I do not know how to reconcile the script where my shells do damage with the script where the zombies take damage. The relevant parts of each script are below:

For ZombieInstance.cs, which is a component of the zombie itself:

     public void Damage(float dmg){
         /*HERE YOU CALL DAMAGE FOR ZOMBIE EXAMPLE: 
         *zombieObject.SendMessage("ZombieDamage", float value, SendMessageOptions.RequireReceiver);
         */
         hp -= dmg;
 
         if(player != null)
             chasePlayer();
 
         if(hp < 0.0f || hp == 0.0f){//This zombie is freakin' dead!
             this.tag = "Untagged";
             BroadcastMessage("ActivateR", SendMessageOptions.RequireReceiver);//Activate ragdoll or spawn the dead bodie.
             Anim.enabled = false;//Deactivate things that might screw the ragdoll up.
             agent.enabled = false;
             GetComponent<Collider>().enabled = false;
             Destroy(gameObject, bodieRemovalTime);
             enabled = false;
         }
     }

For ShellExplosion.cs, which is a component of the shell that explodes and deals damage over a radius from the center of the explosion:

         public void OnTriggerEnter (Collider other)
         {
             // Collect all the colliders in a sphere from the shell's current position to a radius of the explosion radius.
             Collider[] colliders = Physics.OverlapSphere (transform.position, m_ExplosionRadius, m_TankMask);
 
             // Go through all the colliders...
             for (int i = 0; i < colliders.Length; i++)
             {
                 // ... and find their rigidbody.
                 Rigidbody targetRigidbody = colliders[i].GetComponent<Rigidbody> ();
 
                 // If they don't have a rigidbody, go on to the next collider.
                 if (!targetRigidbody)
                     continue;
 
                 // Add an explosion force.
                 targetRigidbody.AddExplosionForce (m_ExplosionForce, transform.position, m_ExplosionRadius);
 
                 // Find the TankHealth script associated with the rigidbody.
                 ZombieInstance targetHealth = targetRigidbody.GetComponent<ZombieInstance> ();
 
                 // If there is no TankHealth script attached to the gameobject, go on to the next collider.
                 if (!targetHealth)
                     continue;
 
                 // Calculate the amount of damage the target should take based on it's distance from the shell.
                 float damage = CalculateDamage (targetRigidbody.position);
 
                 // Deal this damage to the tank.
                 targetHealth.Damage (damage);
 
                 targetHealth.SendMessage("Damage", damage, SendMessageOptions.DontRequireReceiver);
             }
 
             // Unparent the particles from the shell.
             m_ExplosionParticles.transform.parent = null;
 
             // Play the particle system.
             m_ExplosionParticles.Play();
 
             // Play the explosion sound effect.
             m_ExplosionAudio.Play();
 
             // Once the particles have finished, destroy the gameobject they are on.
             Destroy (m_ExplosionParticles.gameObject, m_ExplosionParticles.duration);
 
             // Destroy the shell.
             Destroy (gameObject);
         }
 
 
         public float CalculateDamage (Vector3 targetPosition)
         {
             // Create a vector from the shell to the target.
             Vector3 explosionToTarget = targetPosition - transform.position;
 
             // Calculate the distance from the shell to the target.
             float explosionDistance = explosionToTarget.magnitude;
 
             // Calculate the proportion of the maximum distance (the explosionRadius) the target is away.
             float relativeDistance = (m_ExplosionRadius - explosionDistance) / m_ExplosionRadius;
 
             // Calculate damage as this proportion of the maximum possible damage.
             float damage = relativeDistance * m_MaxDamage;
 
             // Make sure that the minimum damage is always 0.
             damage = Mathf.Max (0f, damage);
 
             return damage;
         }

I want the damage calculated in the ShellExplosion to affect the zombie's health. How can I change my code to make this work? Thanks in advance.