To build a road, 30% of the road was repaired on the first day, 40 meters on the second day, and half of the total length was repaired in two days. How long is this road in meters?
修一条公路，第一天修了30%，第二天修了40米，两天正好修了全长的一半，这条路全长多少米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(1/2) - (3/10)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">40 / (1/5)</gadget>
<output>200</output>

<result>200</result>