Mom bought a "Story Book" for 18.17 yuan and a pencil case for 9.94 yuan, and paid the cashier 50 yuan. How much should I get back?
妈妈买了一本18.17元的《故事书》和一个9.94元的笔盒，付给收银员50元，应找回多少元钱？
<gadget id="calculator">18.17 + 9.94</gadget>
<output>28.11</output>

<gadget id="calculator">50 - 28.11</gadget>
<output>21.89</output>

<result>21.89</result>