Correspondent A travels from base A to base B, and correspondent B travels from base B to base A. Both of them set off at the same time. They met for the first time at a distance of 40 kilometers from base B. After delivering the letters, they both returned by the same route, but they met for the second time at a distance of 50 kilometers from base A. So, what is the distance in kilometers from base A to base B?
甲通信员从A基地到B基地，乙通信员从B基地到A基地，两人同时出发．他们第一次在距B基地40千米处相遇，两人把信件送到后都立即按原路返回，结果在距A基地50千米处第二次相遇．那么，A基地到B基地的距离是多少千米．
<gadget id="calculator">40 * 3</gadget>
<output>120</output>

<gadget id="calculator">120 - 50</gadget>
<output>70</output>

<result>70</result>