The library originally had 710 science and technology books, 230 were borrowed by students, and 140 were returned. How many books are there in the library now?
图书馆原有科技书710本，学生借出了230本，又还回了140本，图书馆现在有图书多少本？
<gadget id="calculator">710 - 230</gadget>
<output>480</output>

<gadget id="calculator">480 + 140</gadget>
<output>620</output>

<result>620</result>