A pencil case is 12.5 yuan, a pen is 6.8 yuan, and there are obviously 20 yuan, how much should I get back for a pencil case and a pen?
一个文具盒12.5元，一支钢笔6.8元，明明有20元，买一个文具盒和一支钢笔应找回多少元？
<gadget id="calculator">12.5 + 6.8</gadget>
<output>19.3</output>

<gadget id="calculator">20 - 19.3</gadget>
<output>0.7</output>

<result>0.7</result>