To build a road, the ratio of the repaired to the unrepaired is 1:5. After another 490 meters have been repaired, the ratio of the repaired to the unrepaired is 3:1. How many meters are left to be repaired?
修一条路，已修的与未修的比是1：5，又修了490米后，已修与未修的比是3：1，这时还剩下多少米未修．
<gadget id="calculator">3 + 1</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>

<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">840 * (1/4)</gadget>
<output>210</output>

<result>210</result>