licensing concern, SAP SQL Anywhere, Workgroup edition

hi folks, I have a licensing question:

I have a client who has 10 full time users and 10 additional part time users, for a total of max 20 users at any one time.  The temp users may rotate, throughout the year.  The server is a 1 CPU, 4 cores.  What is the best licensing model for SAP SQL Anywhere 17, Workgroup Edition, for this scenario, for a Delphi app, connecting to the server for these users?

thanks much,

Cos