Avanti said to Master Bayi: One day, I met a camel merchant from City A, City B, and the camel caravan set off from City B to meet me. The two of us met at a distance of 18 kilometers from the midpoint of City A and City B. The speed ratio of the two of us is 7:4. Master Bai, please help me to calculate, what is the distance between city A and city B?
阿凡提对巴依老爷说：有一天，我从A城区B城和一个骆驼商人见面，骆驼商队从B城出发和我相对而行．我们两个人在距离A城和B城中点18千米处相遇了．我们两个人的速度之比7：4．巴依老爷请你帮我算一算，A城和B城之间的距离是多少呀？
<gadget id="calculator">7 + 4</gadget>
<output>11</output>

<gadget id="calculator">7 / 11</gadget>
<output>7/11 = around 0.636364</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(7/11) - (1/2)</gadget>
<output>3/22 = around 0.136364</output>

<gadget id="calculator">18 / (3/22)</gadget>
<output>132</output>

<result>132</result>