Space Shooter No Definition

I’m writing the tutorial space shooter, and I am attempting to use the method AddScore from the GameController class.

Here is the method:

public void AddScore(int newScoreValue) {
		score += newScoreValue;
		UpdateScore ();
	}

Then, in the DestroyByContact class i am trying to access it like this:

public GameController gameController;
public int scoreValue;

gameController.AddScore (scoreValue);

In the console this error reads:

Assets/Scripts/DestroyByContact.cs(23,32): error CS1061: Type `GameController' does not contain a definition for `AddScore' and no extension method `AddScore' of type `GameController' could be found (are you missing a using directive or an assembly reference?)

Anyone know why this might be?
thanks

public class DestroyByContact : MonoBehaviour {
GameController gameController;
GameObject obj;
public int scoreValue;
void Start(){
obj = GameObject.Find (“the name of the object that GameController script attached to”);
if (obj != null) {
gameController= obj.GetComponent ();
gameController.AddScore (scoreValue);
}
else {
print (“no object with the given name found did you gave the exact name”);
}
}
}