Teacher Zhang went to the bookstore and bought 3 copies of the same book, paid 100 yuan, and got 7.9 yuan back. How much is the price of each book?
张老师到书店买了3本同样的书，付出100元，找回7.9元．每本书的售价是多少元？
<gadget id="calculator">100 - 7.9</gadget>
<output>92.1</output>

<gadget id="calculator">92.1 / 3</gadget>
<output>30.7</output>

<result>30.7</result>