A bottle of AD calcium milk is 3.5 yuan, and a bottle of milk is 6.8 yuan. Mom bought a bottle of AD calcium milk and a bottle of yogurt for Lingling, and paid 20 yuan. How much should I get back?
一瓶AD钙奶3.5元，一瓶牛奶6.8元，妈妈给玲玲买了一瓶AD钙奶和一瓶酸牛奶，付了20元，应找回多少钱？
<gadget id="calculator">3.5 + 6.8</gadget>
<output>10.3</output>

<gadget id="calculator">20 - 10.3</gadget>
<output>9.7</output>

<result>9.7</result>