Two people, A and B, start from AB at the same time and walk towards each other. The speed ratio of A and B is 3:4. It is known that A travels the entire distance (1/3), and is 20 kilometers away from the meeting place. How many kilometers is the distance between AB and AB?
甲乙二人从AB两地同时出发相向而行，甲乙速度比是3：4，已知甲行全程的(1/3)，离相遇地点20千米，AB两地相距多少千米？
<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(3/7) - (1/3)</gadget>
<output>2/21 = around 0.095238</output>

<gadget id="calculator">20 / (2/21)</gadget>
<output>210</output>

<result>210</result>