Mr. Li bought three books, the prices were 7.80 yuan, 5.65 yuan, and 6.20 yuan. He paid 20 yuan, how much should he get back?
李老师买了三本书，价格分别是7.80元、5.65元、6.20元，他付出20元钱，应找回多少钱？
<gadget id="calculator">7.8 + 5.65 + 6.2</gadget>
<output>19.65</output>

<gadget id="calculator">20 - 19.65</gadget>
<output>0.35</output>

<result>0.35</result>