A survey was taken among 100 people to find their preference of watching T. V. programs. There are 3 channels. Given the number of people who watch � At least channel 1 � At least channel 2 � At least channel 3 � No channels at all � At least channels 1and 3 � At least channels 1 and 2 � At least channels 2 and 3 Find the number of people who watched all three.