Little Doctor of Mathematics: The road construction team repaired a section of railway. After one day of repairing, the ratio of repaired to unrepaired was 1:4. The next day after repairing 3200 meters, the ratio of repaired to unrepaired was 5:4. How long is the railway in meters?
数学小博士：修路队修一段铁路，修了一天后，已修和未修的比是1：4，第二天修3200米，这时已修和未修的比是5：4，这段铁路长多少米．
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">1 + 4</gadget>
<output>5</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(5/9) - (1/5)</gadget>
<output>16/45 = around 0.355556</output>

<gadget id="calculator">3_200 / (16/45)</gadget>
<output>9_000</output>

<result>9_000</result>