Perhaps it's as easy as a simple story problem. We already know that there was a coal shortage at the time due to the strike. One must imagine that the Titanic had "ample" coal to complete her journey. I haven't double checked these numbers, so forgive me if they are inaccurate, but there were 29 boilers, 4 of which, I believe, were not lit until later in the voyage. It would be a simple matter of determining how much coal each boiler burned every hour. This number would vary depending on the speed of the Titanic. Then we must determine how many service hours the Titanic should have had, minus the actual service hours the boilers had...and voila. Of course, I have no idea how much coal the boilers needed per hour in comparison to how much coal a ship had on board.
Of course, this information is probably on record somewhere, but I thought this sounded like algebra, so I wanted to make everybody's head hurt...did it work?