Teacher Li bought 8 pens and shared it for 120 yuan, and bought 9 ballpoint pens and shared it for 36 yuan. How much is each fountain pen more expensive than each ballpoint pen?
李老师买8支钢笔共用去120元，买9支圆珠笔共用去36元．每支钢笔比每支圆珠笔贵多少元？
<gadget id="calculator">120 / 8</gadget>
<output>15</output>

<gadget id="calculator">36 / 9</gadget>
<output>4</output>

<gadget id="calculator">15 - 4</gadget>
<output>11</output>

<result>11</result>