@GRADES   = qw( E  D- D  D+ C- C  C+ B- B  B+ A- A  );
@BRACKETS =   (    60,64,67,70,74,77,80,84,87,90,95 );


if ($possible) {
  $average = sprintf("%2.2f", ($earned / $possible) * 100);

  $grade = 0;
  foreach (@BRACKETS) { $grade++ if ($average >= $_); }
  $grade = $GRADES[$grade];

} else {

  $grade = $average = $earned = $possible = "?";
}