Xiao Ming goes to buy the same kind of pen and the same kind of eraser, and the money he brings can buy 8 pens and 4 erasers, or 6 pens and 12 erasers. As a result, he used all the money to buy pens, how many pens he could buy.
小明去买同一种笔和同一种橡皮，所带的钱能买8支笔和4块橡皮，或买6支笔和12块橡皮．结果他用这些钱全部买了笔，他能买多少支．
<gadget id="calculator">12 - 4</gadget>
<output>8</output>

<gadget id="calculator">8 - 6</gadget>
<output>2</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 / 4</gadget>
<output>1</output>

<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<result>9</result>