A and B dig a cave. After team A dug 30% of the total length alone, team B continues to dig alone. When team B dug 210 kilometers, the remaining distance is exactly the distance dug. How many thousand kilometers is the total length of this cave? rice?
甲乙挖一个山洞，甲队单独挖了全长的30%后，乙队接着单独挖，乙队挖了210千米时，剩下路程正好是挖好的路程，这条山洞全长有多少千米？
<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">210 / (1/5)</gadget>
<output>1_050</output>

<result>1_050</result>