sub the_problem {
	my $self = shift;
	$self->{_the_problem} = shift if (@_); # sets _the_problem to the value we've been passed *if* we've been passed a value
	$self->{_the_problem}; # returns the current value of _the_problem
}

##</code><code>##

use strict;
use A::B::C; #use your modules.  Pay attention to btrott's advice above on Exporter etc.
...

my $foo = new A::B::C;
$foo->the_problem("argle bargle"); # $foo->{_the_problem} now eq 'argle bargle'

print $foo->the_problem(); 	# prints "argle bargle"