Xiaojun bought two books, among which "Story King" is priced at 6.3 yuan, and "Fairy Tale World" is priced at 7.8 yuan. After he paid one piece of RMB, the salesperson got back 5.9 yuan. Do you know how much RMB is paid by Xiaojun? (calculate with a calculator)
小军买了两本书，其中《故事大王》售价6.3元，《童话世界》售价7.8元．他付出一张人民币后，营业员找回5.9元．你知道小军付出的是一张面额多少元的人民币吗？(用计算器计算)
<gadget id="calculator">6.3 + 7.8 + 5.9</gadget>
<output>20</output>

<result>20</result>