On a highway, a car starts from the east city to the west city. At this time, A, B, and C start off at the same time in the west city. The speed of A and B is the same, and the speed of C is twice that of A. C goes west, A travels 5 kilometers and meets a car. After meeting, the car catches up with B in 15 minutes, and catches up with C in another 15 minutes. Find the distance between the two cities.
在一条公路上，汽车从东城出发向西城开去，这时西城有甲、乙、丙三人同时出发，甲、乙两人速度相同，丙速是甲的2倍，甲向东，乙、丙向西，甲行5千米与汽车相遇，相遇后汽车经过15分钟追上乙，再过15分钟追上丙，求两城间距离．
<gadget id="calculator">15 + 15</gadget>
<output>30</output>

<result>30</result>