To build a road, the full length (2/5) was built on the first day, and 10.5 kilometers was repaired on the second day. The ratio of the remaining length to the repaired length is 1:3. How many kilometers is the total length of this road?
修一条公路，第一天修了全长的(2/5)，第二天修了10.5千米，剩下的与已修的长度比为1：3，这条公路全长多少千米？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(3/4) - (2/5)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">10.5 / (7/20)</gadget>
<output>30</output>

<result>30</result>