Here is a small example that hints answers towards both of your questions.

#!c:/perl/bin
use Tk;
use strict;
my $main = MainWindow->new();
my $value;
#
# here is an example of how to catch the key return.
# Again, this is just an example, but you will
# see that you get into the calc() function every time
# the user presses enter.

$main->bind('<Key-Return>', \&calc);
# O/K now that the Enter key is bound to the
# window, let's bind $value to the Scale and
# also give Scale a function where we can access
# it's members (e.g. the value of $value)
$main->Scale('orient' => 'horizontal',
             '-from' => 0,
             '-to' => 12,
             '-tickinterval' => 1,
             '-label' => 'Select Time Table',
             '-variable' => \$value,
             '-command' => \&calc)->pack;
MainLoop;

sub calc {
    # remember this is just an example.
    # This prints to the console, but
    # it shows that you have access to the value.
    print $value . "\n";
    #
    # Now that you're in the function, I'll leave
    # it up to you how to do the calculations, and
    # draw up/print a new question.
    # just know that you still have access to all of the
    # widgets that are part of the MainWindow. 
}
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