I am learner in perl, i have question here please help me out

i have some files which contains data like below:

input

file 1
STD    Area    Name    Amount
2    1    AB    1.0    
2    2    AB-1    2.0
4    1    AB-4    1.0    
4    2    AB-6    2.0
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file 2
STD    Area    Name    Amount
21    01    AB    4.0    
22    12    AB-1    6.0
41    44    AB-4    9.0    
42    46    AB-6    4.0
42    46    AB-6    4.0
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file 3
STD    Area    Name    Amount
01    10    AB    4.0    
20    02    AB-1    6.0
40    04    AB-4    9.0    
02    26    AB-6    4.0
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file 4
STD    Area    Name    Amount
56    01    AB    4.0    
56    12    AB-1    6.0
65    44    AB-4    9.0    
65    46    AB-6    4.0
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Output:
    file 1 file 2 file 3    file 4 
AB     1.0    4.0    4.0    4.0
AB-1     2.0    6.0    6.0    6.0
AB-4     1.0    9.0    9.0    9.0
AB-6     2.0    8.0    4.0    4.0
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Each file contains common name where i need to add the Amount. can you please let me know how can i do this.

i tired as mentioned below:

my %result;
my %hash = ( '2.1','AB',
'2.2','AB-1',
'4.1','AB-4',
'4.2','AB-6',
'21.01','AB',
'22.12','AB-1',
'41.44','AB-4',
'42.46','AB-6',
'42.46','AB-6',
'01.10','AB',
'20.02','AB-1',
'40.04','AB-4',
'02.26','AB-6',
'56.01','AB',
'56.12','AB-1',
'65.44','AB-4',
'65.46','AB-6');

foreach my $file (@files) {
open FILE, "<$dir/$file" or warn "Couldn't open file ($!) or file ($!)
+ not found\n";
while (chomp ( my @fields = split /\t/, <FILE>) ) {    
my $key = "$fields[0].$fields[1]";

if (exists $hash{$key})
{
$key = $hash{$key};

if (exists($result{$key}))
{
$result{$key} += $fields[03];
}
else { 
$result{$key} += $fields[03];
}
}
}
}
close FILE;
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