Two cars, A and B, start from two places AB at the same time and drive back and forth between AB. It is known that the speed of A car is 30 kilometers per hour, and the speed of B car is 70 kilometers per hour. Well and The place where the two cars A and B meet for the third time is exactly 100 kilometers away from the place where they met for the fourth time. How many miles is the distance between A and B?
甲、乙两辆汽车，分别从AB两地同时相向出发，在AB之间不断返行驶，已知甲车的速度是每小时30千米，乙车的速度是每小时70千米，井且甲乙两车第三次相遇的地点与第四次相遇的地点恰好相距100千米．AB两地相距多少千米？
<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<gadget id="calculator">3 + 7</gadget>
<output>10</output>

<gadget id="calculator">15 - 10</gadget>
<output>5</output>

<gadget id="calculator">3 * 7</gadget>
<output>21</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">21 - 20</gadget>
<output>1</output>

<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">100 / 4</gadget>
<output>25</output>

<gadget id="calculator">25 * 10</gadget>
<output>250</output>

<result>250</result>