Teacher Wang went to the bookstore and bought a copy of "One Hundred Thousand Whys" and a copy of "Xinhua Dictionary". How much should I get back?
王老师到书店买了一本《十万个为什么》和一本，《新华字典》付给售货员100元，一本《十万个为什么》20.90元，一本《新华字典》16.80元．应找回多少元？
<gadget id="calculator">20.9 + 16.8</gadget>
<output>37.7</output>

<gadget id="calculator">100 - 37.7</gadget>
<output>62.3</output>

<result>62.3</result>