A company needs to transport 1000 units of product from a factory located in City A to a warehouse located in City B. The distance between City A and City B is 500km. The company has two options for transportation: by truck or by train. The truck has a maximum capacity of 200 units and can travel at an average speed of 80km/h. The train has a maximum capacity of 500 units and can travel at an average speed of 120km/h. The cost of using the truck is $2 per unit, while the cost of using the train is $1.5 per unit.

a) Calculate the number of truck trips required to transport all the units from City A to City B.
b) Calculate the number of train trips required to transport all the units from City A to City B.
c) Calculate the total cost of using the truck to transport all the units from City A to City B.
d) Calculate the total cost of using the train to transport all the units from City A to City B.
e) Which transportation method would you recommend to the company based on the cost and time required? Justify your answer.