How to perform calculations based on variables from 2 different instances of a object

Im currently trying to write a damage calculation script (not assigned to any game object) that calls the variables from 2 different instances that collided with each other, for example:

bullet1.cs

using UnityEngine;
using System.Collections;

public class bullet1 : MonoBehaviour {

	public float Damage = 10;

	void OnCollisionEnter(Collision target){
		if (target.gameObject.tag == "TargetHeadShot"){
			damageCalc.Calculation(bullet1, target);
		}
	}
}

targetData.cs

using UnityEngine;
using System.Collections;

public class targetData : MonoBehaviour {

	public float maxHp = 100;
	public float curHp = 100;
	public GUITexture hpBar;
	public float hpBarLength;
	public float hpPercent;
}

damageCalc.cs

using UnityEngine;
using System.Collections;

public class damageCalc : MonoBehaviour {

	void Calculation(object bullet, object enemy){
		/*does the calculations here as well as destroying the bullet and subtracting hp from enemy*/
	}
}

however, i get a error saying:

Assets/bullet1.cs(19,36): error CS0120: An object reference is required to access non-static member `damageCalc.Calculation(object, object)'

is it even possible to do this? thanks in advance!

You need to get reference to the specific instance of ‘damageCalc’ attached to ‘target’.

target.gameObject.GetComponent<damageCalc>().Calculation(bullet1, target);

Note by convention class names and functions names should start with upper case letters.