A building with 4 floors, each floor is divided as follows; 15 users for accounting, 15 users for finance and 15 users for marketing (i.e 45 user in each floor).

Data center is located on the ground floor, with 45 servers to be divided into 15 for all the accounting users in the four floors, another 15 for the finance and the last 15 for the marketing. (i.e each 15 server for each one of the above categories are separated from the other 15 and so on)

What is the proper subnetting design for such scenario? Knowing that we are allowed to use anything we want!