A car travels from A to B, and after driving for 1 hour, the ratio of the traveled distance to the total distance is 1:3. If it travels another 15 kilometers, it will just arrive at the midpoint of the two places. How many kilometers is the distance between the two places?
一辆车从甲地到乙地，行驶1小时后，已行路程与总路程的比为1：3，如果再行驶15千米，就正好到达两地的中点．两地间相距多少千米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/2) - (1/3)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">15 / (1/6)</gadget>
<output>90</output>

<result>90</result>