There are 4 identical bookcases in Xiaogang’s study room, and each bookcase holds 138 books. How many books can these 4 bookcases hold in total?
小刚家的书房有4个同样的书柜，每个书柜放138本书，这4个书柜一共可以放多少书？
<gadget id="calculator">138 * 4</gadget>
<output>552</output>

<result>552</result>