convenience store buys a new batch of biscuits, and the profit from selling 12 boxes at a price of 8 yuan per box is the same as the profit from selling 9 boxes at a price of 9 yuan each. What is the purchase price of each box of biscuits?
便利店新购入一批饼干，按每盒8元定价卖出12盒的利润，与按每个9元定价卖出9盒的利润相同．则每盒饼干的进价是多少元．
<gadget id="calculator">8 * 12</gadget>
<output>96</output>

<gadget id="calculator">9 * 9</gadget>
<output>81</output>

<gadget id="calculator">96 - 81</gadget>
<output>15</output>

<gadget id="calculator">12 - 9</gadget>
<output>3</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<result>5</result>