Two people, A and B, ride bicycles towards each other from the east and west towns at the same time. The speed ratio of A and B is 3:4. It is known that when A travels (1/3) of the whole journey, there is still 20 kilometers away from the meeting place. How many kilometers did A travel less than B when they met?
甲、乙两人同时骑自行车从东西两镇相向而行，甲乙速度的比是3：4，已知甲行了全程的(1/3)时，离相遇地点还有20千米．相遇时甲比乙少行多少千米？
<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>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">(4/7) - (3/7)</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">210 * (1/7)</gadget>
<output>30</output>

<result>30</result>