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.