this is my code:

bool ch=Type.IsBuiltIn("System.Int32");   // not working-> syntax error


public static class MyExtentions
    {             
        public static bool IsBuiltIn(this Type t, string _type)
        {
            return (Type.GetType(_type) == null) ? false : true;
        }
    }

Please I want Extend Type Class by IsBuiltIn new method