For a road, the ratio of the repaired to the unrepaired is 3:7. After another 300m is repaired, the repaired will account for 50% of the unrepaired. Find the total length of this road?
一条路，已修的和未修的比是3：7，再修300m后，已修的就占未修的50%，求这条路的全长？
<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 + (1/2)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">(1/2) / (3/2)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">3 + 7</gadget>
<output>10</output>

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

<gadget id="calculator">(1/3) - (3/10)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">300 / (1/30)</gadget>
<output>9_000</output>

<result>9_000</result>