I need help with a Grade Distrubution Table in PHP

[system]

I need to have the user be able to input as many grades as they want. And then run a table with 3 colums,
col 1-A number ID 1 to whatever
col 2- the number grade entered
col 3-the letter grade that goes with the number grade

Here is my form entry page

Grade Distribution Table

Grade Distribution Table Entry Form

ENTER GRADES INTO THE BOX BELOW
SEPERATE EACH SCORE WITH A COMMA
(E.G. 90,78,89,70,100)
Please Enter Grades Here:

Here is my php logic

Grade Distribution Table

MSIS 2203 Grade Distribution Table

<?php $Scores=array($_POST['Grades']); $Explode=explode(",",'$Scores'); $Counter=count($Scores); $ID=0; while ($ID<=$Counter) { $ID++; } if ($Scores<=100 && $Scores>=90) { $LetterGrade="A"; } elseif ($Scores<=89 && $Scores>=80) { $LetterGrade="B"; } elseif ($Scores<=79 && $Scores>=70) { $LetterGrade="C"; } elseif ($Scores<=69 && $Scores>=60) { $LetterGrade="D"; } else { $LetterGrade="F"; } ?>

Student ID	Scores	Letter Grade
<?php print "$ID" ?>	<?php print "$Scores"?>	<?php print "$LetterGrade" ?>

The mean test score was:

The maximum test score was:

The minimum test score was: