I have a good idea how to solve this work problem, and that is down one of the 4 ways listed below, but I am not sure, can you direct me to which expression would be the proper one?

A behavioral economist studies transportation habits in an urban center. She identifies 4 bus routes that connect to 3 different light rail routes available to participants in the study. Before she interviews participants, she must determine the number of possible routes participants can choose to use. Which expression represents the number of available options? It would be

4!+3! or 43 or 4!/3! or 4!3!

Thank you for your help. cm/1