Three processes A, B and C are admitted into the ready queue by the long-term scheduler. The processes are admitted -- first process C, then B, and then A -- without any delay between the admissions. The short-term scheduler uses a Round-Robin scheduling policy to assign processes to run on the CPU. The time quantum is ns. The CPU burst times ns, ns and ns (for  A, B and C respectively) are all multiples of . Assume , the processes make no I/O requests, and all of the processes successfully complete. You may also assume that no other processes or OS activity are important for your computations. 

Based only on the information given, which of the following formulae is the average turnaround time for these 3 processes? 

Hint: to deduce which of these formulae is correct, check which formula gives the same answer you got earlier for the average turnaround related to a C,B,A order of arrivals.