A, B, and C each buy a batch of exercise books together at 9 yuan. Since A is 15 less than C at the time of distribution, and B and C want the same amount, B and C each have to give A 1.5 yuan ． How many exercise books did the three of them buy together?
甲、乙、丙三人各出9元合伙买了一批练习本，由于分配时甲比丙少15本，乙和丙要的一样多，因此，乙和丙每人都要给甲1.5元．三人合伙买了多少本练习本？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">15 * (2/3)</gadget>
<output>10</output>

<gadget id="calculator">15 - 10</gadget>
<output>5</output>

<gadget id="calculator">1.5 / 5</gadget>
<output>0.3</output>

<gadget id="calculator">3 / 0.3</gadget>
<output>10</output>

<gadget id="calculator">9 * 10</gadget>
<output>90</output>

<result>90</result>