In shewak's opinion, his weight is greater than 76 kg but less than 83 kg. His sister doest not agree with shewak and she thinks that shewak’s weight is greater than 71 kg but less than 81 kg. His father's view is that his weight cannot be greater than 79 kg. If all are them are correct in their estimation, what is the average of different probable weights of shewak? A) 67kg B) 68kg C) 72kg D) 78kg