Computer Science · Operating Systems

Consider four processes P, Q, R, and S scheduled on a CPU as per the round-robin algorithm with a time quantum of 4 units. The processes arrive in the order P, Q, R, S, all at time t = 0. There is exactly one context switch from S to Q, exactly one context switch from R to Q, and exactly two context switches from Q to R. There is no context switch from S to P. Switching to a re ady process after the termination of another process is also considered a context switch. Which one of the following is NOT possible as the CPU burst time (in time units) of these processes?