The stationery store bought a batch of small balls at a wholesale price of 0.35 yuan each, and sold them at a retail price of 0.45 yuan. When there were 30 small balls left, the stationery store had made a profit of 12 yuan. The stationery store bought small balls how many?
文具商店以每个0.35元的批发价购进一批小皮球，将0.45元的零售价卖出，当卖到还剩下30个小皮球时，已获利12元，文具商店购进小皮球多少个？
<gadget id="calculator">30 * 0.45</gadget>
<output>13.5</output>

<gadget id="calculator">13.5 + 12</gadget>
<output>25.5</output>

<gadget id="calculator">0.45 - 0.35</gadget>
<output>0.1</output>

<gadget id="calculator">25.5 / 0.1</gadget>
<output>255</output>

<result>255</result>