since, n=7
therefore we will send first, 1,2,3,4,5*,6,7 but according to question 5th packet would be lost
so from the fifth, we will need to send another frame of 7 packets but we only have 3 packets left 8,9,10
so the next frame will be 5,6,7*,8,9,10 but here again 5th packet will be lost ,counting start from when the last packet was lost(5)
now again send next frame 7,8*,9,10 counting starting from last lost packet (7)
next frame will be 8,9,10* counting start from last lost packet(8)
at last 10 will be sent alone. Thus completing the whole transfer.
1,2,3,4,5*6,7 5,6,7*,8,9,10 7,8*,9,10 8,9,10* 10
total =21
extra=total - packets=> 21-10=11.