Xiao Pang went to the school supplies store and bought 3 exercise books with the same price and 4 fountain pens with a unit price of 2.9 yuan, which cost 20 yuan in total. How much is each exercise book?
小胖去学习用品商店买了3本价格相同的练习本和4支单价2.9元的水笔，一共用去20元．练习本每本多少元？
<gadget id="calculator">2.9 * 4</gadget>
<output>11.6</output>

<gadget id="calculator">20 - 11.6</gadget>
<output>8.4</output>

<gadget id="calculator">8.4 / 3</gadget>
<output>2.8</output>

<result>2.8</result>