Xiao Li travels from city A to city B at a speed of 50 km/h, and Xiao Lan travels from city B to city A at a speed of 40 km/h. The two started at the same time, and they met at a distance of 10 kilometers from the midpoint of A and B. Find the distance between cities A and B.
小李从A城到B城，速度是50千米/小时，小兰从B城到A城，速度是40千米/小时．两人同时出发，结果在距A、B两城中点10千米处相遇．求A、B两城间的距离．
<gadget id="calculator">10 + 10</gadget>
<output>20</output>

<gadget id="calculator">50 - 40</gadget>
<output>10</output>

<gadget id="calculator">20 / 10</gadget>
<output>2</output>

<gadget id="calculator">50 + 40</gadget>
<output>90</output>

<gadget id="calculator">2 * 90</gadget>
<output>180</output>

<result>180</result>