The first class bought 2 fountain pens and 5 ballpoint pens for 39 yuan to distribute the prizes; the second class bought the same 3 fountain pens and 4 ballpoint pens for 48 yuan. How much is a pen more expensive than a ballpoint pen?
为发奖品一班用39元买了2支钢笔，5支圆珠笔；二班48元买了同样的3支钢笔，4支圆珠笔，一支钢笔比一支圆珠笔贵多少元？
<gadget id="calculator">39 * 3</gadget>
<output>117</output>

<gadget id="calculator">48 * 2</gadget>
<output>96</output>

<gadget id="calculator">117 - 96</gadget>
<output>21</output>

<gadget id="calculator">3 * 5</gadget>
<output>15</output>

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

<gadget id="calculator">15 - 8</gadget>
<output>7</output>

<gadget id="calculator">21 / 7</gadget>
<output>3</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">39 - 15</gadget>
<output>24</output>

<gadget id="calculator">24 / 2</gadget>
<output>12</output>

<gadget id="calculator">12 - 3</gadget>
<output>9</output>

<result>9</result>