Given Data :
bit rate = 128 Kbps
round trip time(2Tp) = 40 msec
Therefore Tp = 20 msec
length of one frame = 512 Bytes = 512*8 bits
Transmission Time = length / bandwidth = 512*8 / (128kbps) = 32msec
efficiency = (Tt / Tt + 2Tp) = 32 / (32 + 2*40) = 0.44444444
Answer :
Efficiency percentage = 44.44 %