or you can do it something like this

use strict;
use warnings;

my @pence=qw(5 10 20 50);
my @notes=qw(5 10 20 50);

my ($sum1, $sum2);
foreach my  $c (@pence){
    print "How many $c pence pieces do you have? ";
    my $num=<STDIN>;
    chomp $num;
    my $res = ($c * $num)/100;
     $sum1  += $res;
    
}
foreach my $n (@notes){
    print "How many &#321;$n notes do you have? ";
    my $num=<STDIN>;
    chomp $num;
    my $res = ($n * $num);
     $sum2 += $res;
}
my $final =$sum1+$sum2;
    print "You are ritch, you have $final coins!!!!!";
[download]

it is a bit longer but intuitive.