Sliding window is of two types:

'1.) Go Back N

2.) Selective Repeat

if we consider here Go Back N, then ans would be 15 as window size= (2^k)-1 i.e. (2^4)-1=16-1=15

but if we consider Selective Repeat then ans would be 8 as window size= 2^(k-1) i.e. 2^(4-1)=2^3=8

so why we considering here only Go Back N only, not Selective Repeat.. ?

'1.) Go Back N

2.) Selective Repeat

if we consider here Go Back N, then ans would be 15 as window size= (2^k)-1 i.e. (2^4)-1=16-1=15

but if we consider Selective Repeat then ans would be 8 as window size= 2^(k-1) i.e. 2^(4-1)=2^3=8

so why we considering here only Go Back N only, not Selective Repeat.. ?