To build a road, the whole length (1/4) is repaired for the first time, and the whole length (3/20) is repaired for the second time. At this time, there is still 6 kilometers away from the midpoint of the road. How long is this road?
修一条公路，第一次修全程的(1/4)，第二次又修全程的(3/20)，这时距公路的中点还有6千米．这条公路有多长？
<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">3 / 20</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(1/4) + (3/20)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/2) - (2/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">6 / (1/10)</gadget>
<output>60</output>

<result>60</result>