There is a batch of goods at the station, and it is planned to be transported 21 times. If 4 tons are transported each time, the number of times will be reduced by 6 times. How many tons is this shipment?
车站有一批货物，计划21次运完，如果每次多运4吨，次数就减少6次．这批货物有多少吨？
<gadget id="calculator">4 * 21</gadget>
<output>84</output>

<gadget id="calculator">4 * 6</gadget>
<output>24</output>

<gadget id="calculator">84 - 24</gadget>
<output>60</output>

<gadget id="calculator">1 / 21</gadget>
<output>1/21 = around 0.047619</output>

<gadget id="calculator">(1/21) * 6</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(1/21) * 21</gadget>
<output>1</output>

<gadget id="calculator">(2/7) - 1</gadget>
<output>-5/7 = around -0.714286</output>

<gadget id="calculator">1 + (-5/7)</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">60 / (2/7)</gadget>
<output>210</output>

<result>210</result>