##

foreach (values $ARGS{LineItem}) {
    $SQL->execute(
        $PONum,
        $ARGS{"first-${i}"},
        $ARGS{"second-${i}"},
        $ARGS{"third-${i}"}
    );
}

##

##

my @lineitems = $ARGS{"LineItem"};
foreach my $line (@lineitems) {
print "line is @$line[0]";
print $ARGS{"first-@$line[0]"};
print $ARGS{"second-@$line[0]"};
print $ARGS{"third-@$line[0]"};

}