...
my $sumcredits;
while (my $pimrpt = <PM>) {
...
  $sumcredits+= $credits;
...
}
print "The sum of credits is $sumcredits\n";

##</code><code>##

...
my %sumcredits;
while (my $pimrpt = <PM>) {
...
  $sumcredits{$company}+= $credits;
...
}
foreach my $comp (keys %sumcredits) {
  print "The sum of credits for $comp is $sumcredits{$comp}\n";
}