LRTF means the process which has remaining time largest will run first and in case of same remaining time lowest process_id will be given priority to run.
First 4 sec ,P2 will run . then P2 remaining time =4 ,p1=4,p0=2.
Now P1 will get chance to run for 1 sec. P2=4,p1=3,p0=2.
Now p2 will get chance to run for 1 sec, P2=3,p1=3,p0=2.
This way if we do carefully, TAT of P1 will be 14 sec,p1=13 sec and p0= 12 sec.
Total TAT = 14+13+12= 39
Avg TAT= 39/3 =13 sec.