public function multiply($a, $b, $c, $d, $e, $f) 
    {
        return new Matrix(
            $this->a * $a + $this->c * $b,
            $this->b * $a + $this->d * $b,
            $this->a * $c + $this->c * $d,
            $this->b * $c + $this->d * $d,
            $this->a * $e + $this->c * $f + $this->e,
            $this->b * $e + $this->d * $f + $this->f
        );
    }