Wang Hong bought a fountain pen with a unit price of 13.5 yuan. She bought 7 pens and paid 100 yuan. How much did she get back?
王红买了单价是13.5元的钢笔，买了7支，付了100元，她找回了多少钱？
<gadget id="calculator">13.5 * 7</gadget>
<output>94.5</output>

<gadget id="calculator">100 - 94.5</gadget>
<output>5.5</output>

<result>5.5</result>