Xiao Wang and Xiao Li spent the same amount of money to buy exercise books, but Xiao Wang took 12 books, 8 more than Xiao Li, so Xiao Wang gave Xiao Li another 8.4 yuan. How much is each exercise book?
小王和小李拿出同样多的钱买练习本，结果小王拿了12本，比小李多拿了8本，所以小王又给了小李8.4元．每本练习本多少元？
<gadget id="calculator">12 - 8</gadget>
<output>4</output>

<gadget id="calculator">12 + 4</gadget>
<output>16</output>

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">8.4 / 4</gadget>
<output>2.1</output>

<result>2.1</result>