A Go$-$Back$-$N scheme has a frame with a $6$ Byte header and is using the optimal frame size with a probability of bit error of $12$ in a million, or $0\mathrm{.}000012.$ The transmission rate is $2$Mb$/$s on the link $.$ The propagation delay in both directions is $88$us $($micro$-$seconds$)$ and the processing time is the same at the sender and receiver and is $400$us $($micro$-$seconds$)$ for each.

The ACK is $6$ Bytes and is being sent back on its own. The Transmission time of this must be considered. However the assumption is that there is no error in the ACK and the optimal Timeout is chosen.

What is the percentage efficiency of this system in percentage? Round your answer.