There are 78 story books in the small library. After borrowing 2 books, the number of story books is exactly 4 times that of the science books. How many science books are there?
小小图书室有78本故事书，借掉2本书后，故事书的本数正好是科技书的4倍，科技书有几本？
<gadget id="calculator">78 - 2</gadget>
<output>76</output>

<gadget id="calculator">76 / 4</gadget>
<output>19</output>

<result>19</result>