Suppose Po burst time is x unit, P0 run for 5 units of time before getting preempted by P2, therefore remaining time = x-5 unit
P2 burst time is y unit, P2 runs for 2 units of time before getting preempted by P1, therefore remaining time = y-2
P1 run for 4 unit fo time.
Since P1 preempt P2, and SRTF is used so minimum value of P2 must be 5 unit at that time, so y-2 = 5 i.e y = 7
Similarly x-5 = 8, and x = 13 unit.
So minimum burst time of P0 is 13 unit