Two trains run from east to west at the same time. It takes 10 hours for train A to go from east city to west city, and 8 hours for train B to travel from west city to east city. After 2.5 hours, the distance between the two trains is 35 kilometers. How many kilometers is the distance between the east and west cities?
两列火车同时从东西两城相对开，甲车从东城到西城需10小时，乙车从西城到东城需8小时，2.5小时后两车相距35千米，东西两城相距多少千米？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(1/10) + (1/8)</gadget>
<output>9/40 = around 0.225</output>

<gadget id="calculator">(9/40) * 2.5</gadget>
<output>0.5625</output>

<gadget id="calculator">1 - 0.5625</gadget>
<output>0.4375</output>

<gadget id="calculator">35 / 0.4375</gadget>
<output>80</output>

<result>80</result>