Shortest Job First (SJF):
$$\begin{array}{|c|c|c|} \hline \textbf{Process Name} & \textbf{AT} & \textbf{BT} & \textbf{CT} & \textbf{TAT}
\\\hline P_{1} & 0 & 10 & 29 & 29
\\\hline P_{2} & 0 & 9 & 19 & 19
\\\hline P_{3} & 0 & 4 & 4 & 4
\\\hline P_{4} & 0 & 6 & 10 & 10
\\\hline \end{array}$$
$\text{Turn around time = Completion time – Arrival time}$
Grantt chart:
Average turn around time $ = \dfrac{29+19+4+10}{4} = \dfrac{62}{4} = 15.5\;\text{msec}$
Round robin scheduling with time quantum $ = 5\;\text{msec}:$
$$\begin{array}{|c|c|c|} \hline \textbf{Process Name} & \textbf{AT} & \textbf{BT} & \textbf{CT} & \textbf{TAT}
\\\hline P_{1} & 0 & 10 & 24 & 24
\\\hline P_{2} & 0 & 9 & 28 & 28
\\\hline P_{3} & 0 & 4 & 14 & 14
\\\hline P_{4} & 0 & 6 & 29 & 29
\\\hline \end{array}$$
$\text{Turn around time = Completion time – Arrival time}$
Queue$:P_{1}P_{2}P_{3}P_{4}P_{1}P_{2}P_{4}$
Grantt chart:
Average turn around time $ = \dfrac{ 24+28+14+29}{4} = \dfrac{95}{4} = 23.75\;\text{msec}$
The difference between the average turnaround times (in ms) of SJF and RR $ = \mid 15.5 – 23.75 \mid = \mid – 8.25 \mid = 8.25\;\text{msec}.$
So, the correct answer is $8.25\;\text{msec}.$