The school library originally had 674 science and technology books, 253 of which were lent out, and 137 were returned. How many science and technology books are there in the library now?
学校图书室原有科技书674本，借出253本，还回137本，现在图书室有多少本科技书？
<gadget id="calculator">674 - 253</gadget>
<output>421</output>

<gadget id="calculator">421 + 37</gadget>
<output>458</output>

<result>458</result>