A second try


my $width = 30 * 0.3048;
my $length = 50 * 0.3048;
my $radius = 10 * 0.0254;
my $rate = 1000 / 10000;

my $cost = $rate *
    ($width*$length - 3.14159*$radius**2);

print "Cost is: $cost\n";