It takes a car 9 hours to travel from A to B, and only 7 hours to return from B to A. It is known that the return travel is 10 kilometers per hour longer than that of the departure, how many kilometers is the distance between A and B?
一辆汽车从甲地到乙地用了9小时，从乙地返回甲地只用了7小时．已知返回时比去时每小时多行10千米，甲、乙两地相距多少千米？
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(1/7) - (1/9)</gadget>
<output>2/63 = around 0.031746</output>

<gadget id="calculator">10 / (2/63)</gadget>
<output>315</output>

<result>315</result>