The pencil case is 12 yuan each, and the notebook is 7 yuan each. I bought a total of 6 and spent 52 yuan. How many pencil boxes should I buy?
文具盒每个12元，笔记本每个7元，共买了6个，用了52元，文具盒买多少个．
<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>