If you bring 50 yuan to the bookstore, the comic book costs 7.8 yuan, the popular science books cost 12.6 yuan, the literature and art books cost 9.3 yuan, and the supplementary books cost 10.5 yuan. formula answer.
如果你带50元去书店，连环画要7.8元，科普读物要12.6元，文艺书要9.3元，教辅书要10.5元，根据这些图书的价格，编一道两步加、减法计算的问题，并列式解答．
<gadget id="calculator">7.8 + 10.5</gadget>
<output>18.3</output>

<gadget id="calculator">50 - 18.3</gadget>
<output>31.7</output>

<result>31.7</result>