#!/usr/bin/perl
use strict; 
use warnings;

my @myarray = (2.5 ,4.8, 3.2, 8.5, 8.2, 12.5);
my %value_map;

my $counter = @myarray;
for my $key (sort {$b <=> $a} @myarray) {
    $value_map{$key} = $key*6/$counter--;
}

for my $key (@myarray) {
    print "$key\t-> $value_map{$key}\n";
}