bandwidth of the network is 64 Mbps
average packet size is of 8 Kb
distance between two system =4000 kilometers
transmission time Tt=8*1024/64*106=128*10-6 s
propagation time Tp=4000*1000 meter/1.5*3*108 m/s=20 ms
maximum window size=1+2a
=1+2*20 ms/128*10-6 s = 1+2* 20*10-3 s /128*10-6 s =313.5
in SRA protocol sender window size=receiver window size
sequence no=2* window size =2*313.5=627
so sequence bit =log(627)=10 bits