my @data = (
           ["1.6","2.2","3.4","3.6","5.4","6.2","7.1", "8.1", "9.0"],
           [    1,    2,    5,    6,    3,  15,    4,     3,     4],
           [ sort { $a <=> $b } (1, 2, 5, 6, 3, 15, 4, 3, 4) ]
         );

print join(", ", @{$data[1]}), "\n";

map { $data[1]->[$_]++ if $data[0]->[$_] =~ /3.4/ } 0..$#{$data[0]};

print join(", ", @{$data[1]}), "\n";

--(0)> perl test.pl
1, 2, 5, 6, 3, 15, 4, 3, 4
1, 2, 6, 6, 3, 15, 4, 3, 4