time starts at t=0, then 1st packet sent will leave A at t = 8ms
time starts at t=8, then 2nd packet sent will leave A at t = 16ms
time starts at t=16, then 3rd packet sent will leave A at t = 24ms
time starts at t=24, then 4th packet sent will leave A at t = 32ms
time starts at t=32, then 5th packet sent will leave A at t = 40ms
therefore at t = 40ms, All packets left A
at t= 40 + 20, last packet reach R1 ==> at t=60
Now last packet leave the R1 at t = 60+8 = 68
at t= 68 + 20, last packet reach R2 ==> at t=88
Now last packet leave the R2 at t = 88+8 = 96
at t= 96 + 20, last packet reach R1 ==> at t=116