Currently we're 3 workers in our Systems Department, the thing is the three of us do everything: support(for a bit over 75 users, and a bit over 90 computer systems[some computers are used by 2 or 3 different users]), software development, networking, database administration(for over 9 small companies), and sometimes look for manuals and such for other departments, one of the guys is leaving now, and my colleague and I feel like the department lacks structure, I know that being able to do everything is good experience wise, but it's bad performance wise as in we can't really focus on one thing since we also have to be by the phone whenever a user encounters a problem. We want to convince our CFO(since he alongside the member that's leaving, helped to digitize the company and that's why our department reports to him, that's what I was told) that we need an extra worker with a degree and at least 3 interns, but the CFO is very jealous when it comes to spending money, how can I convince him that it's not only money being spent but more of an investment for the company?
Note that my colleague has been 1 year and 1 month on the job and I have been around for 9 months. So we're relatively new and don't feel like our recommendations/suggestions have enough weight to be considered.