Final answer:
A trackman reporting a fire should immediately provide the location and size of the fire. The time is also important, but the cause of the fire can be determined later and is not critical to the initial response.
Step-by-step explanation:
When a trackman discovers a fire at the end of a station platform and reports it to the trainmaster, the essential information that should be immediately communicated includes the location of the fire, and if possible, the size of the fire, since these details are critical for a timely and effective emergency response.
While the time of the fire may also be important to understand the urgency and to coordinate the response, the cause of the fire is less critical to be communicated at the moment of urgency and can be investigated once the fire is under control. The cause of the fire is not necessary for the initial report and can be determined later through investigation.