Problem with creating static bool...

I can’t call this:

using UnityEngine;
using System.Collections;

public static class VarToUtilities {
	public static bool StringToBool(this string RecievedText) {
		if(RecievedText == "true"){
			return true;
		}else if(RecievedText == "True"){
			return true;
		}else if(RecievedText == "false"){
			return false;
		}else if(RecievedText == "False"){
			return false;
		}else if(RecievedText == "no"){
			return false;
		}else if(RecievedText == "No"){
			return false;
		}else if(RecievedText == "yes"){
			return true;
		}else if(RecievedText == "Yes"){
			return true;
		}
		return false;
	}
}

with this code:

using UnityEngine;
using System.Collections;

public class Tester : MonoBehaviour {
	public string ExampleString;
	public bool ExampleBool;

	void Update () {
		ExampleBool = StringToBool(ExampleString);
	}
}

How to get this work? Please help!

As explained in comments, you need a fully qualified name:

ExampleBool = VarToUtilities.StringToBool(ExampleString);