1km = 5 microsec so 1000km = 5*1000 microsec
RTT = L/B + 2 * PropagationTime
here L is packet size
and B is bandwidth
RTT = (1250 * 8 bits)/109 bits + 2*5000 microsec
= 10micro sec + 10000micro sec
= 10010 microsec
No of packets = (Bandwidth * delay)/packet size
=(109 * 10010 *10-6) / (1250 * 8)
= 1001