There are 990 storybooks in the school library, 429 are lent out in the morning and 310 in the afternoon, how many storybooks are left in the library?
学校图书馆有990本故事书，上午借出429本，下午借出310本，图书馆还剩多少本故事书．
<gadget id="calculator">429 + 310</gadget>
<output>739</output>

<gadget id="calculator">990 - 739</gadget>
<output>251</output>

<result>251</result>