The bookstore implements a preferential measure for customers: 5% discount for each purchase of books between 200 and 500 yuan, and 10% discount for each purchase of more than 500 yuan. A customer buys three books in a bookstore, and the price of each book does not exceed 250 yuan. If the first and second purchases are combined, it is 13.5 yuan cheaper than buying them separately; the three mergers are 39.4 yuan cheaper than the three separate purchases. ． May I ask how much the customer bought the book for the third time?
书店对顾客实行一项优惠措施：每次买书200元至500元者优惠5%，每次买500元以上者优惠10%．某顾客到书店买了三次书，每次的书价都不超过250元，如果第一次与第二次合并一起买，比分开买便宜13.5元；三次合并一起买比三次分开买便宜39.4元．请问这位顾客第三次买了多少钱的书？
<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">13.5 / (1/20)</gadget>
<output>270</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">270 * (1/10)</gadget>
<output>27</output>

<gadget id="calculator">39.4 - 27</gadget>
<output>12.4</output>

<gadget id="calculator">(1/10) - (1/20)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">12.4 / (1/20)</gadget>
<output>248</output>

<result>248</result>