Aspace station sounds an alert signal at time intervals of 1.80 h . spaceships a and b pass the station, both moving at 0.400c0 relative to the station but in opposite directions. part a how long is the time interval between signals according to an observer on a? express your answer in hours. δtaδ t a = nothing h request answer part b how long is the time interval between signals according to an observer on b? express your answer in hours. δtbδ t b = nothing h request answer part c at what speed must a move relative to the station in order to measure a time interval of 3.60 h between signals? express your answer in terms of c0. vav a = nothing.