Can someone explain each line?

#! usr/bin/perl

print “Enter the Quiz score: “;

$quiz = <>;

print “Enter the Activity score: “;

$classactivities = <>;

print “Enter the homework score: “;

$homework = <>;

print “Enter the labs score: “;

$labs = <>;

print “Enter the discussion score: “;

$discussion = <>;

print “Enter the exams score: “;

$exams = <>;

my %hash = ($quiz,

$classactivities,

$homework,

$labs,

$discussion,

$exams );

my @scores = (65,67,78,90); #array of number

my $returned_values;

$returned_values = sum(@scores); #calling sum function

print “sum value = $returned_values n”;

$returned_values = percent(5,20); #pass any value here

print “percent value = $returned_values n”;

$returned_values = grade(72);

print “grade $returned_valuesn”;

sub sum{

my @score_list = @_; #parameters are stored in @_

my $result = 0;

for (@score_list) {

$result = $result + $_; #computing sum

}

return $result;

}

sub percent{

my($first,$second) = @_;

my $result = ($first*100)/$second;

return $result;

}

sub grade{

my $percentage = $_[0];

return “unknown grade” if($percentage > 100); #passed value is greated then 100

return “A+” if($percentage >= 95.0 and $percentage <= 100.0);

return “A” if($percentage >= 90.0 and $percentage <= 95.0);

return “A-” if($percentage >= 87.5 and $percentage <= 90.0);

return “B+” if($percentage >= 85.0 and $percentage <= 87.5);

return “B” if($percentage >= 82.5 and $percentage <= 85.0);

return “B-” if($percentage >= 80.0 and $percentage <= 82.5);

return “C+” if($percentage >= 77.5 and $percentage <= 80.0);

return “C” if($percentage >= 70.0 and $percentage <= 77.5);

return “D” if($percentage >= 60.0 and $percentage <= 70.0);

return “F” if($percentage <= 60.0);

}