Uncle Li packed 840 toys in 5 large boxes and 6 small boxes. One large box contained the same number of toys as 3 small boxes. How many toys did each small box hold?
李叔叔把840件玩具分别装在5个大箱和6个小箱里，1个大箱与3个小箱装的玩具同样多，每个小箱装多少件玩具？
<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">15 + 6</gadget>
<output>21</output>

<gadget id="calculator">840 / 21</gadget>
<output>40</output>

<result>40</result>