> I need some help with substrings in JavaScript.?

I need some help with substrings in JavaScript.?

Posted at: 2014-12-18 
"wonderful day".substring(3, 7);

I'm learning how to program with JavaScript on code academy (www.codeacademy.com) and it says to find the 4th the to the 7th letter of the string "wonderful day" I've tried everything, and I'm quite sure that I get it but for some reason none of my answers seem to be correct. I've tried (3,6) but that didn't work. And I've been stuck on this for days.