Question

A passenger sitting in a train A moving at (v) observes another train B moving in the opposite direction for (Δ t). If the velocity of train B is (u), then the length of train B is:
a) (v ⋅ Δ t)
b) (u ⋅ Δ t)
c) (v + u)
d) (u ⋅ Δ tv)