Two ships, A and B, set off at the same time from ports A and B, which are 150 kilometers apart, and head toward each other. A is the upstream port, and B is the downstream port. The speed is 10km/h. The two ships meet at point C, and then both ships arrive at their respective destinations. The next day, A returns to port A from port B, and B returns to port B from port A. The two ships are at point D. Meet, ask for the distance between C and D.
甲、乙两船分别从相距150千米的A、B两港同时出发，相向而行，A是上游港口，B是下游港口，甲船的静水速度是20千km/h，乙船的静水速度是10km/h，两船在C点相遇，之后两船都到达了各自的目的地，第二天甲从B港回到A港，乙从A港回到B港，两船在D点相遇，请求出C、D两点的距离．
<result>50</result>