use strict;
use warnings;

use Data::Dumper;

my %hash = (
    one => [ 1, 2, 4 ], 
    two => [ 5, 7, 9 ],
);

my @add = ( 7, 8, 15 );

$hash{one} = [ map { $hash{one}{$_} + $add[$_] } (0 .. $#add) ];

print Dumper \%hash;