".135 days later in his frame, at "t′" = 270 + 135 = 405, he calculates that since the tachyon signal has been traveling away from him at 2.4"c" in the −"x′" direction for 135 days, it should now be at position "x′" = −2.4×135 = −324 light-days in his frame, and since Alice has been traveling at 0.8"c" in the −"x" direction for 405 days, she should now be at position "x′" = −0.8×405 = −324 light-days as well.So, in his frame Alice receives his reply at "x′" = −324, "t′" = 405.