A fountain pen is 5.5 yuan, which is 2.15 yuan more expensive than a ballpoint pen. Teacher Zhang bought a fountain pen and a ballpoint pen and paid the salesperson 20 yuan. How much should I get back?
一枝钢笔5.5元，比一枝圆珠笔贵2.15元，张老师买了一枝钢笔和一枝圆珠笔，付给售货员20元，应找回多少元？
<gadget id="calculator">5.5 - 2.15</gadget>
<output>3.35</output>

<gadget id="calculator">3.35 + 5.5</gadget>
<output>8.85</output>

<gadget id="calculator">20 - 8.85</gadget>
<output>11.15</output>

<result>11.15</result>