use strict;
use warnings;

my $factor = 0.5;
my $base = -15;
my $base2 = -8;

result( "$base * $factor", $base * $factor );

result( "$base2 + $base * $factor", $base2 + $base * $factor );

# Show a result.
# Pass it 2 args:
# ARG1: display string to inform user about the calculation.
# ARG2: displayed as a float, 2 place precision.
sub result {
	printf "%s is: %.2f\n", shift // '', shift // 0;
}