First of calculate the Maximum packets that we can send : 1+2*a
= 1 + 2*170/60
= 1+ 5.6
= 6.6 = 6
It means if the window size is 6 then we get 100% throughput
but here we only send 4 packets
therefore efficiency = 4/6 = 0.67
Tt = length of the packet / bandwidth
Bandwidth = 1500 / 60 x 10 -6
= 25000000 bytes per sec
If efficiency is not equal to 1 then it doesn't achieve the 100% then Throughput should decrease but how much ??
Throughput = $\eta$ *Bandwidth
= 0.67 * 25000000
= 16750000 Bytes per sec