Teacher Li has a stack of homework books. If 10 people share 4 books on average, and if 15 people share 4 books on average, how many homework books are there in this stack?
李老师有一叠作业本，如果平均分给10人还剩4本，如果平均分给15人也是剩4本，这叠作业本至少有多少本？
<gadget id="calculator">2 * 3 * 5</gadget>
<output>30</output>

<gadget id="calculator">30 + 4</gadget>
<output>34</output>

<result>34</result>