L=1000 bits
B=1 Mbits/sec
Transmission Delay($T_{t}$)=$\frac{1000}{1*10^6}$=1 ms
Prpagation Delay($T_{p}$)=270 ms
a=$\frac{T_{p}}{T_{t}}=\frac{270}{1}$=270
Frame sequence number=3 bits
(a) Stop & Wait Protocol
Channel Utilization/Efficiency=$\frac{1}{1+2a}$=0.18 %
(b) Go-Back-N Protocol
in GBN, window size of sender=$2^m-1$ where m=sequence number bits
N=$2^3-1$=7
Channel Utilization/Efficiency=$\frac{N}{1+2a}$=1.29%
(c) Selective Repeat Protocol
Window size of sender=window size of receiver=half the available sequence numbers=$2^m/2=2^3/2=4$
N=4
Channel Utilization/Efficiency=$\frac{N}{1+2a}$=0.74%