public function get_matching_answer($value, $multiplier) {
        if (is_null($value) || $value === '') {
            return null;
        }

        if (!is_null($multiplier)) {
            $scaledvalue = $value * $multiplier;
        } else {
            $scaledvalue = $value;
        }
        foreach ($this->answers as $answer) {
            if ($answer->within_tolerance($scaledvalue)) {
                $answer->unitisright = !is_null($multiplier);
                return $answer;
            } else if ($answer->within_tolerance($value)) {
                $answer->unitisright = false;
                return $answer;
            }
        }

        return null;
    }