 And in his frame (difference in position)/(difference in time) for his signal is 324/135 = 2.4"c", exactly the same as the speed of Alice's original signal in her own frame.Likewise, in Alice's frame Bob's signal moves backwards in time (she received it before he sent it), and it has a (difference in position)/(difference in time) of 360/207, about 1.739"c".Thus the times of sending and receiving in each frame, as calculated using the Lorentz transformation, match up with the times given in earlier paragraphs, before we made explicit use of the Lorentz transformation.