A fountain pen is 12.3 yuan, which is 7.5 yuan more expensive than a ballpoint pen. How much does it cost to buy a ballpoint pen?
一支钢笔12.3元，比一支圆珠笔贵7.5元．买一支圆珠笔要用多少元？
<gadget id="calculator">12.3 - 7.5</gadget>
<output>4.8</output>

<result>4.8</result>