The bookstore buys a certain book at a price of 10.08 yuan each, and sells each book at 16.8 yuan. When there are 10 books left, in addition to recovering all costs, it also makes a profit of 504 yuan. How many books of this kind does the bookstore buy?
书店以每本10.08元的价格购进某种图书，每本售价16.8元，卖到还剩10本时，除了收回全部成本外，还获利504元．这个书店购进该种图书多少本．
<gadget id="calculator">16.8 * 10</gadget>
<output>168</output>

<gadget id="calculator">504 + 168</gadget>
<output>672</output>

<gadget id="calculator">16.8 - 10.08</gadget>
<output>6.72</output>

<gadget id="calculator">672 / 6.72</gadget>
<output>100</output>

<result>100</result>