Wang Lan read a story book, and the ratio of the number of pages she has read to the number of pages she has not read is 3:4. If she reads another 39 pages, she has read 80% of the whole book. How many pages does this storybook have?
王岚读了一本故事书，已读的页数与未读的页数之比是3：4，如果再读39页，就读了全书的80%．这本故事书共有多少页？
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">(4/5) - (3/7)</gadget>
<output>13/35 = around 0.371429</output>

<gadget id="calculator">39 / (13/35)</gadget>
<output>105</output>

<result>105</result>