use warnings;
use Tk;

my $mw=MainWindow->new();
$mw->Button(-text=>"   Test   ", -command=>sub{test()}, -font=>'Helvetica 18 bold', -pady=>20)->pack();
MainLoop;

sub test {
  print "result:\n";
  $_A = '16.25'; # string, not number
  $_V = '12.99'; # string, not number
  $formula = 'sprintf("%.0f", ($_V * $_A))';
  $_W = eval($formula);

  print "$_V\n";
  print "$_A\n";
  print "$_W\n";
}