A car travels from A to B at a speed of 30 kilometers per hour. After 4 hours, a train also travels from A to B at a speed of 90 kilometers per hour. At the midpoint between A and B, the train catches up with the car, and ask how many kilometers are the distance between A and B.
一辆汽车以每小时30千米的速度从甲地开往乙地，开出4小时后，一列火车以每小时90千米的速度也从甲地开往乙地．在甲乙两地的中点处火车追上汽车，问甲乙两地相距多少千米．
<gadget id="calculator">90 - 30</gadget>
<output>60</output>

<gadget id="calculator">4 / 60</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">90 * 30 * (1/15) * 2</gadget>
<output>360</output>

<result>360</result>