To build a road, the ratio of the length of the repaired to the unrepaired is 1:4, and after repairing (4/5) kilometers, the ratio of the length of the repaired to the unrepaired is 1:3. How many meters will be repaired to complete the task?
修一条公路，已修的和未修的长度比是1：4，再修(4/5)千米后，已修的和未修的长度的比1：3．还要修多少米才能完成任务？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</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">1 + 4</gadget>
<output>5</output>

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

<gadget id="calculator">(1/4) - (1/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(4/5) / (1/20)</gadget>
<output>16</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">16 * (3/4)</gadget>
<output>12</output>

<result>12</result>