A clothing store buys a batch of children's clothing, and prices each piece at a profit of 40%. When selling 90% of the children's clothes at this price, in order to speed up capital turnover due to the season change, the clothing store will sell them at a discount of 30% of the price and sell all the remaining children's clothes. 15% less profit. According to regulations, regardless of the price at which the children's clothing is sold, the sales tax of 300 yuan must be paid when the children's clothing is sold out. How much did the clothing store spend on buying these children's clothes?
服装店买进一批童装，按每件获得40%的利润定价．按此定价卖出这批童装的90%时，由于换季，为了加快资金周转，服装店按定价的七折出售，将剩下的童装全部卖出，这样所得的利润比按原定价出售获得的利润少了15%．按规定，不论以什么价格出售，卖完这批童装必须上缴营业税300元．服装店买进这批童装花了多少元．
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 + (2/5)</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">1.26 + 0.098</gadget>
<output>1.358</output>

<gadget id="calculator">(7/5) - 1.358</gadget>
<output>0.042</output>

<gadget id="calculator">0.042 / (7/5)</gadget>
<output>0.03</output>

<gadget id="calculator">(3/20) - 0.03</gadget>
<output>0.12</output>

<gadget id="calculator">300 / 0.12</gadget>
<output>2_500</output>

<result>2_500</result>