operating systems – Gantt chart for Round Robin Scheduling using only arrival and completion time

I had the following question in my Operating System ‘CPU- Scheduling’ assignment-

4 processes A,B,C,D have estimated time of completion of 5,7,9,11 ns each. They are scheduled in a round-robin fashion and the time slice is of 2ns. The processes A,B,C,D arrive at the 0,1,2,3 ns respectively. At what time will the process C complete? Also what will be the completion time of process C, if Shortest Job First was used instead of Round Robin?

My doubt is- Can we design a Gantt Chart using just Arrival time and Completion time. I referred many books and websites but in all the places the chart was designed using arrival and burst time rather than completion time.

If I assume the question to be straightforward then I don’t need a Gantt Chart and can easily get the completion time of C to be 9 in round-robin scheduling. However, calculating the completion time for SJF scheduling will become a mystery. I am guessing the question could be printed wrong yet I am not sure and would like some assurance if it’s wrong, else some guidance on how to tackle the above question.