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. The speed of this train is three times that of the car. He caught up with the car at half the distance to B. How many kilometers are there 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，一列火车也从甲地开往乙地，这列火车的速度是汽车的3倍，在甲地到乙地距离二分之一的地方追上了汽车．甲乙两地相距多少千米？
<gadget id="calculator">30 * 3</gadget>
<output>90</output>

<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">30 * 3 * 30 * (1/15) * 2</gadget>
<output>360</output>

<result>360</result>