certain development zone needs to build a road. The first phase is 50% of the total length, and the second phase is 30% of the total length. The first phase is 0.8 kilometers longer than the second phase. What is the total length of this road in kilometers?
某开发区要修一条公路，第一期修了全长的50%，第二期修了全长的30%，第一期比第二期多修了0.8千米．这条公路的全长是多少千米？
<gadget id="calculator">50 / 100</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">0.8 / (1/5)</gadget>
<output>4</output>

<result>4</result>