They do use error carried forward, I'm pretty sure, although the question you are referring to seems ambiguous.
You obviously used the contracted length to figure out the time. This uses the previous answer so I imagine error carried forward would apply.
My only doubt is that part b can be done without the use of part a, since t=d/s which are both given to you in the question [1x10^7** and 0.99999c]. If you did it this way, I imagine error carried forward would not apply. :S
Toughie... Will the markers use ECF for one method and not the other, or not use it for both or use it for both... You get what I'm saying lol?
** or whatever it was =)