Xiaopang went to the store to buy exercise books, and the money he brought was 1.80 yuan more for 4 books, and the 6 books were just used up. How much is each exercise book?
小胖去商店买练习本，他带的钱买4本还多1.80元，买6本正好用完，每本练习本多少钱？
<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<gadget id="calculator">1.8 / 2</gadget>
<output>0.9</output>

<result>0.9</result>