I am stuck on the Challenge to Create a formula field that returns an image to indicate data quality. It's in the Text Formulas module of Advanced Formulas badge.

No matter what I try, I can't pass the Syntax checker. I am required to display a certain number of stars based on Data Quality calculated in another formula. And include alternate text. (By the way, is there any way to trace formulas, so I could see the number being returned by the data quality formula?)

Herer's my formula . . . 

IMAGE
(CASE(Lead_Quality_Helper__c ,
5, ("/img/samples/stars_500.gif", "5 Stars",)
4, ("/img/samples/stars_400.gif", "4 Stars",)
3, ("/img/samples/stars_300.gif", "3 Stars",)
2, ("/img/samples/stars_200.gif", "2 Stars",)
1, ("/img/samples/stars_100.gif", "1 Stars",)
0, ("/img/samples/stars_000.gif", "0 Stars",)
"Unknown"))

IMAGE can take two parameters. The URL and the ALTERNATE TEXT. So I put both parameters surrounded by (.....). The Syntax checker says I am missing a parenthesis between the URL and the Alternate Text. But inserting one there results in an error that CASE is expecting a number, not text.

What am I doing wrong here?