Given the following four processes, in the order of arrival, and their CPU burst times (in milliseconds):

Process CPU Burst
P1 6
P2 3
P3 7
P4 1

Assuming that context switching takes 1.5 milliseconds, calculate the optimal quantum q in Round Robin scheduling, also in milliseconds, such that the average wait time is minimized.

This is my answer, but I am not sure if it is a correct answer.

Total effective CPU burst time = Total CPU burst time + Total context switch time = 17 + 4.5 = 21.5 milliseconds.
q = Total effective CPU burst time / Number of processes = 21.5 / 4 ≈ 5.375 milliseconds.