Teacher Zhao went to the store to buy office supplies. It cost 17.9 yuan to buy a pen, which is 4.8 yuan more than buying paper. Teacher Zhao gave the salesperson 50 yuan. How much should I get back?
赵老师去商店买办公用品．买笔用去17.9元，比买纸多用4.8元，赵老师给售货员50元，应找回多少元？
<gadget id="calculator">17.9 - 4.8</gadget>
<output>13.1</output>

<gadget id="calculator">17.9 + 13.1</gadget>
<output>31</output>

<gadget id="calculator">50 - 31</gadget>
<output>19</output>

<result>19</result>