A bookstore sells a kind of wall calendar, and can get a profit of 18 yuan for each copy sold. After the bookstore sells a part, each book will be reduced by 10 yuan, until all are sold out. It is known that the number of wall calendars sold is 2/3 of the original price. The bookstore makes a profit of 2,870 yuan after selling this kind of calendar. How many copies of this kind of calendar are sold in the bookstore?
某书店出售一种挂历，每卖出一本可获得18元利润，书店卖出一部分后每本减价10元，直至全部卖完，已知出售的挂历本数是原价出售本数的2/3，书店卖完这种挂历获利润2870元，书店里卖出这种挂历多少本？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(2/3) * 18</gadget>
<output>12</output>

<gadget id="calculator">(2/3) * 10</gadget>
<output>20/3 = around 6.666667</output>

<gadget id="calculator">12 - (20/3)</gadget>
<output>16/3 = around 5.333333</output>

<gadget id="calculator">18 + (16/3)</gadget>
<output>70/3 = around 23.333333</output>

<gadget id="calculator">2_870 / (70/3)</gadget>
<output>123</output>

<gadget id="calculator">123 * (2/3)</gadget>
<output>82</output>

<gadget id="calculator">123 + 82</gadget>
<output>205</output>

<result>205</result>