The library originally had 710 science and technology books, students borrowed 230 and returned 140. How many science and technology books are there in the library?
图书馆原有710本科技书，学生借走了230本，又还回来140本，图书馆现在有多少本科技书？
<gadget id="calculator">710 - 230</gadget>
<output>480</output>

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

<result>620</result>