Xiao Dingding went to the store and bought 4 exercise books with the same price and 3 ballpoint pens with a unit price of 3.5 yuan. The total cost was 13.7 yuan. How much is each exercise book?
小丁丁去商店买了4本价格相同的练习本和3支单价3.5元的原珠笔，一共用去13.7元，练习本每本多少元？
<gadget id="calculator">3.5 * 3</gadget>
<output>10.5</output>

<gadget id="calculator">13.7 - 10.5</gadget>
<output>3.2</output>

<gadget id="calculator">3.2 / 4</gadget>
<output>0.8</output>

<result>0.8</result>