My approach is :
I calculated utilization first which is the time when link is active by total time
U = transmission/ total time
Transmission = 1.048msec
Since no ack sort of policy is used so total time = transmission + propagation
U = 1.048/51.048 = 0.0205
Throughout = 0.0205 × 1GBps = nearly 161Mbps
What's wrong answer is B by the way