Xiaoliang plans to write 100 words in 3 days. He wrote 29 yesterday and 42 today. How many words will he write tomorrow?
小亮计划3天写100个字，昨天写了29个，今天要写42个，明天要写多少个字？
<gadget id="calculator">29 + 42</gadget>
<output>71</output>

<gadget id="calculator">100 - 71</gadget>
<output>29</output>

<result>29</result>