The train speed is 1 1 times that of A, so their relative speed is 10 times that of A. It takes 18 seconds to pass through A and 15 seconds to pass through B, so the relative speed of the train and B is10 */kloc. That is to say, the speed of B is actually the same as that of A. So the relative speed of A and B is twice that of A, so the distance from the train meeting A and then meeting B is 138* 12/2=828 seconds, minus 18+ 15=33 seconds.