my $days = 72;
my $firstday = 5;
# for each 7 days each element gets a value of +1
# initialise 8 array elements
my @daycounts = (int($days/7)) x 8; 
$days = $days%7;

for my $day_num( ($firstday-1) .. ($days+$firstday-2) ) {
    $daycounts[1+$day_num%7]++;
}

# now print it out nice and pretty

my %weekdays = (
    1 => Monday,
    2 => Tuesday,
    3 => Wednesday,
    4 => Thursday,
    5 => Friday,
    6 => Saturday,
    7 => Sunday);

for my $day_num(1..7) {
    print "$daycounts[$day_num]\t$weekdays{$day_num}\n";
}

# here it is as a one liner
$daycounts[1+$_%7]++ for ($firstday-1)..($days+$firstday-2);