A steel factory produced 8,400 tons of steel in April, and the output in May was 1/7 more than that in April. The sum of the output of the two months is exactly 75% of the planned output in the second quarter. What is the planned output in the second quarter?
某钢厂四月份产钢8400吨，五月份比四月份多产(1/7)，两个月产量和正好是第二季度计划产量的75%，则第二季度计划产钢多少吨．
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 + 1 + (1/7)</gadget>
<output>15/7 = around 2.142857</output>

<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(15/7) / (3/4)</gadget>
<output>20/7 = around 2.857143</output>

<gadget id="calculator">8_400 * (20/7)</gadget>
<output>24_000</output>

<result>24_000</result>