Since the radii of the circles are 40m and 80m respectively, the circumference would be 80pi and 160pi meters respectively.
Since N’s speed is 40pm/ min, he would take 4 minutes to cover a round. This also means that when M starts running, they would both be at point R, since N would have covered 1 round exactly in 4 minutes.
Also, for the straight-line distance to be 240 m they should be at the diametrically opposite ends from the point R (of their respective circles).
M reaches the diametrically opposite end (from R) of his circle for the first time in 30 seconds and after that he would reach the same point every 1 minute at 1:30, 2:30 and so on.
N on the other hand would reach the diametrically opposite end at 2 minutes, 6 minutes, 10 minutes and so on.
They would never be exactly 240 m apart.
Option (d) is correct.