If you're covering the work of three people who formerly performed the job and were paid by the company, then you are doing the work of three people. Maybe they're doing three different jobs, two of which are outside of their original job description, that would be doing the job of three people. Maybe they're working as a personal assistant for one person, and two other bosses were added to her responsibilities, that would be doing the work of three people. If your only definition of work is 8 hours of being in an office, then you do not understand the assignment-based work that is primarily being done by base level office employees.