To build a road, the full length (1/3) was built on the first day, and the full length (1/4) was built on the second day, leaving 210 kilometers to be repaired. How long is this road in kilometers?
修一条公路，第一天修了全长的(1/3)，第二天修了全长的(1/4)，还剩210千米没修．这条公路全长多少千米？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/3) + (1/4)</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">1 - (7/12)</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">210 / (5/12)</gadget>
<output>504</output>

<result>504</result>