The cost of two commodities, A and B, is 3,000 yuan. Commodity A is priced at 40% of the profit, and commodity B is priced at 30% of the profit. Both commodities are sold at 90% of the price, resulting in a profit of 690 yuan. How much is the cost of commodity A?
甲、乙两种商品成本共3000元，甲商品按40%的利润定价，乙商品按30%的利润定价，两种商品都按定价的90%出售，结果获利690元．甲种商品的成本是多少元？
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">3_000 * (9/10)</gadget>
<output>2_700</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">3_000 * (3/10) * (9/10)</gadget>
<output>810</output>

<gadget id="calculator">690 - 2_700 - 810</gadget>
<output>-2_820</output>

<gadget id="calculator">3_000 + (-2_820)</gadget>
<output>180</output>

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

<gadget id="calculator">(2/5) * (9/10)</gadget>
<output>9/25 = around 0.36</output>

<gadget id="calculator">(3/10) * (9/10)</gadget>
<output>27/100 = around 0.27</output>

<gadget id="calculator">(9/25) - (9/10) - (27/100)</gadget>
<output>-81/100 = around -0.81</output>

<gadget id="calculator">(9/10) + (-81/100)</gadget>
<output>9/100 = around 0.09</output>

<gadget id="calculator">180 / (9/100)</gadget>
<output>2_000</output>

<result>2_000</result>