The ratio of the repaired length to the unrepaired length is 1:5. After 490 meters are repaired, the ratio of the repaired length to the unrepaired length is 3. What is the total length of this road?
已经修的和未修的长度比是1：5，再修490米后，已修的长度与未修的长度比值是3，这条路全长有多少？
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

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

<gadget id="calculator">1 + 5</gadget>
<output>6</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(3/4) - (1/6)</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">490 / (7/12)</gadget>
<output>840</output>

<result>840</result>