We know that D = T × V, where D is the distance, T is the time, and V is the velocity or speed.
In other words, T = D / V. We insert the corresponding values to find the time needed for a bit to travel the cable.
T = D / V = (2500 meters) / (200,000,000 meters/second) = 0.0000125 s = 12.5 μs