here, the transmission delay is 2KB/109bps =2*103*8/109=16 micro seconds
total propagation delay = (250+250)m /500,000 kmps=1 micro second (counting the total length of both links together)
here, the packet is transmitted twice into the medium, once from A to link1 and second from R to link 2. so the transmission time is calculated twice.
so total time=2*transmission time + propagation time+ queing delay time
=2*16 + 1 + 7=40 micro second
ANS 40 micro second