The express train and the local train depart from the east and west stations at the same time, and meet for the first time at 10 kilometers west of the midpoint. After the encounter, the two cars move forward at the same speed. When they met, the distance from the east station accounted for three-sevenths of the distance between the two stations. How many kilometers is the distance between the east and west stations?
快车和慢车同时从东西两站相对开出，第一次在距中点西侧10千米处相遇，相遇后两车以原速前进，到达东西两地后，两车立即返回，第二次相遇时离东站的距离占两站距离的七分之三．东西两站相距多少千米？
<gadget id="calculator">10 * 2 * 3</gadget>
<output>60</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 - (3/7)</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">60 / (1/7)</gadget>
<output>420</output>

<result>420</result>