Based on the following passage, answer the Questions :
A $3000 \mathrm{~km}$ long trunk operates at $1.536 \mathrm{mbps}$ and is used to transmit 64 bytes frames and uses sliding window protocol. The propagation speed is $6 \mu \mathrm{sec} / \mathrm{km}$.
The sender window size to get the maximum efficiency is
- $108$
- $109$
- $55$
- $56$