Duration of time between the first time and the last time the light was seen = 3 hr 17 min 49 sec - 1 hr 54 min 50 sec
=(3×3600+17×60+49)sec−(3600+54×60+50)sec
=11869sec–6890sec =4979sec It is given that the light was seenregularly at an interval of 13 seconds. Therefore, the number of times the light was seen =