The engineering team builds a road, the ratio of the length of the repaired to the unrepaired is 1:5, after another 490 meters, the ratio of the length of the repaired to the unrepaired is exactly 3. How long is this road in meters?
工程队修一条路，已修的和未修的长度比是1：5，再修490米后，已修的与未修的长度是比值恰好是3．这条路全长多少米？
<gadget id="calculator">1 + 5</gadget>
<output>6</output>

<gadget id="calculator">5 / 6</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">1 + 3</gadget>
<output>4</output>

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

<gadget id="calculator">(5/6) - (1/4)</gadget>
<output>7/12 = around 0.583333</output>

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

<result>840</result>