There are 4 rows of willow trees planted by the lake, each row has 891 willow trees. How many willow trees are there in total?
湖边种着4排柳树，每排891棵，一共有多少棵柳树？
<gadget id="calculator">891 * 4</gadget>
<output>3_564</output>

<result>3_564</result>