A and B start from A and B at the same time and walk toward each other, and meet at a distance of 15 kilometers from the midpoint. It is known that the speed ratio of A and B is 3:4. How many kilometers are there between A and B?
甲乙两人同时从A、B两地出发相向而行，在距中点15千米处相遇．已知甲乙速度比为3：4．A、B两地相距多少千米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<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">(1/2) - (3/7)</gadget>
<output>1/14 = around 0.071429</output>

<gadget id="calculator">15 / (1/14)</gadget>
<output>210</output>

<result>210</result>