advertising window=36KB
1 maximum segment size=2KB
tp=100ms
RTT=2tp=200ms
window receiver=36KB/2KB=18 segment(at max it can recive)
threshold=36KB/2KB=18KB
NOW
1SEG| 2seg| 4seg | 8seg| 9seg | 10seg | 11seg| 12 seg | 13 seg| 14 seg| 15seg | 16seg| 17seg| 18seg
2KB | 4KB| 8KB | 16KB| 18KB| 20KB | 22KB | 24KB | 26KB | 28KB | 30KB | 32KB| 34KB| 36KB
so after 13 RTT sender sendes its first max no segment to receiver....
therefore 13*200=2600ms ans. according to me