use strict;
use warnings;
use 5.010;
use Math::Expression::Evaluator;

my $m = Math::Expression::Evaluator->new;
# read all the variables
$m->parse("x1=3.8; x2=5.8; x3=4.1; y1=10.1; y2=11.6; y3=12.7")->val;

# do the calculations you are interested in:
say $m->parse("x1 *  x2")->val;