From City A to City B, it takes 10 hours for a bus to complete the journey, and 15 hours for a truck to complete the journey. If two vehicles depart from both cities at the same time, the distance between the two vehicles will be 35 kilometers after 7 hours. How many kilometers are there between the two cities?
从甲城到乙城，客车行完全程要10小时，货车行完全程要15小时，若两车同时从甲乙两城出发，7小时后两车相距35千米．甲乙两城相距多少千米？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/10) + (1/15)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / (1/6)</gadget>
<output>6</output>

<gadget id="calculator">7 - 6</gadget>
<output>1</output>

<gadget id="calculator">1 * (1/6)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">35 / (1/6)</gadget>
<output>210</output>

<result>210</result>