What is the wagons of a train analogy of message length and its relationship with propagation delay calculation under bandwidth and data rates?

a) What is the wagons of a train analogy of message length and its relationship with propagation delay calculation under bandwidth and data rates?
b) What is the wagons of a train analogy of message length and its relationship with propagation delay calculation under bandwidth and data rates?
c) What is the wagons of a train analogy of message length and its relationship with propagation delay calculation under bandwidth and data rates?
d) What is the wagons of a train analogy of message length and its relationship with propagation delay calculation under bandwidth and data rates?