If d is distance measured in km and t is time measured in hours, then d = 69t tells you that train A is moving at a rate of 69 km/h.
Why? If t = 1, then d is the distance it moves in 1 hour, and that's precisely the unit rate. It's the rate at which the distance changes when 1 unit of time passes.
For train B, use the info in the given table. In 1 hour (between hours 4 and 5), the train covers a distance of 375 km - 300 km = 75 km. So it's moving at a rate of 75 km/h.
It should be clear which train is faster.