A train covered a certain distance at a uniform speed

A train covered a certain distance at a uniform speed. If the train had been 6 km/hr faster, it would have taken 4 hour less than the scheduled time. And, if the train were slower by 6 km/hr, the train would have taken 6 hr more than the scheduled time. The length of the journey is:

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #64725