one approach that avoids package variables (and the magical package variables $a and $b) might be (UNTESTED):

my $grandtotal = 0;

foreach my $row (@$array_ref) {
    my ($type, $total) = @$row;
    if ($type =~ m{\A \s* (?: A|B|C|D|W) \s* \z}xms) {
        $grandtotal += $total;
        }
    }
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