A person buys and sells goods from the wholesale market at the same cost each time. If the previous batch of goods is sold out and then buys another batch of goods for sale, if he sets the price at a profit of 20%, it will take an average of 4 months to sell the goods. If the original profit is reduced by 15%, the goods can be sold out one month in advance, so that he can increase his profit by 3080 yuan a year. How much is his cost of shopping each time?
某人每次以相同的成本从批发市场购货物出售，前一批货物卖完接着再购进一批货物出售，如果他以20%的利润定价，平均要4个月才能把货物卖完，如果把原来的利润降低15%，则可以提前一个月将货物卖完，这样他一年反而可以增加利润3080元，他每次购物的成本是多少元．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">1 - (3/20)</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">(17/20) / 3</gadget>
<output>17/60 = around 0.283333</output>

<gadget id="calculator">(1/5) * (17/60)</gadget>
<output>17/300 = around 0.056667</output>

<gadget id="calculator">(1/5) / 4</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(17/300) - (1/20)</gadget>
<output>1/150 = around 0.006667</output>

<gadget id="calculator">3_080 / 12 / (1/150)</gadget>
<output>38_500</output>

<gadget id="calculator">38_500 * 4</gadget>
<output>154_000</output>

<result>154_000</result>