There is a kind of storybook in the bookstore. After selling (3/4), another 210 copies are purchased. At this time, the number of this kind of storybook is more than the original number (1/8). How many copies of this kind of storybook have been sold?
书店有一种故事书，卖出(3/4)后，又购入210本，这时这种故事书的本数比原有本数多(1/8)，这种故事书卖出了多少本？
<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/8) - (1/4)</gadget>
<output>-1/8 = around -0.125</output>

<gadget id="calculator">1 + (-1/8)</gadget>
<output>7/8 = around 0.875</output>

<gadget id="calculator">210 / (7/8)</gadget>
<output>240</output>

<gadget id="calculator">240 * (3/4)</gadget>
<output>180</output>

<result>180</result>