Total time required for K bit delivery = K/ R + 2* RTT = K/R+ 2* ( L* t)
= K/R+ 2Lt
optimal window size = 1+(2 * BW* prop delay)/Frame size = 1+ (2*R*Lt /K)
= (K+2RLt)/K
For maximum utilization window size should be 2^n-1 = (K + 2RLt)/K
2^n = (2K +2RLt)/K
n = log (2K+2RLt)/K
Answer option A