The ratio of the number of books on the bookshelves A and B is 7:5, and 78 books are taken from the A bookshelf to the B bookshelf, and the ratio of the number of books on the A and B bookshelves becomes 3:4. How many volumes of books are there on shelf A?
甲、乙两个书架放图书册数的比是7：5，从甲书架上拿78册到乙书架，甲、乙书架上的图书册数的比变为3：4．甲书架原有图书多少册？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(3/4) * 78</gadget>
<output>117/2 = around 58.5</output>

<gadget id="calculator">78 + (117/2)</gadget>
<output>273/2 = around 136.5</output>

<gadget id="calculator">(3/4) * 5</gadget>
<output>15/4 = around 3.75</output>

<gadget id="calculator">7 - (15/4)</gadget>
<output>13/4 = around 3.25</output>

<gadget id="calculator">(273/2) / (13/4)</gadget>
<output>42</output>

<gadget id="calculator">7 * 42</gadget>
<output>294</output>

<result>294</result>