A man runs around a curved rack as shown below, in which the radius of each semicircle increases by `r` meters. If the man's initial speed is `pi``r` m/s and the man halves his speed after every semicircle track, the time will he take to complete running around the track if there are 8 such semicircles and the smallest has radius `r` is: (a). 22 min 12 sec, (b). 29 min 53 sec, (c). 31 min 37 sec, (d). 37 min 43 sec.