To build a road, the ratio of the length of the repaired to the unrepaired is 2:5, and after 300 meters is repaired, the ratio of the length of the repaired to the unrepaired is 1:2. How many meters is this road?
修一条公路，已修和未修的长度之比是2：5，再修300米之后，已修和未修的长度之比是1：2．这条公路长多少米？
<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">2 + 5</gadget>
<output>7</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(1/3) - (2/7)</gadget>
<output>1/21 = around 0.047619</output>

<gadget id="calculator">300 / (1/21)</gadget>
<output>6_300</output>

<result>6_300</result>