Each fountain pen is 12 yuan, and each ballpoint pen is 7 yuan. I bought 6 pens in total and spent 52 yuan. How many pens did I buy?
钢笔每支12元，圆珠笔每支7元，共买了6支，用了52元，钢笔买了多少支．
<gadget id="calculator">7 * 6</gadget>
<output>42</output>

<gadget id="calculator">52 - 42</gadget>
<output>10</output>

<gadget id="calculator">12 - 7</gadget>
<output>5</output>

<gadget id="calculator">10 / 5</gadget>
<output>2</output>

<result>2</result>