UFOs, Ghosts, and Big Foot

As we know, 2 people believe in all three, so that goes in the middle (union). 4 people believe in UFOs and Big Foot, so the 4 minus the 2 already in the union of all three leaves 2. The same thing can be said for the 11 people that believe in UFOs and Ghosts, 11-2=9; as well as those that believe in Ghosts and Big Foot, 6-2=4. To find out how many only believe in UFOs, we must add together the ones that believe in multiple (9+2+2=13) and subtract the total that believe in just UFOs. This leaves us with 29; (42-13=29). The same can be done for the others and their corresponding intersecting and union circles. Big Foot has 13, for example (4+2+2=8); (21-8=13). While Ghosts have 30, (9+2+4=15); (45-15=30). This leaves us with 72 that believe in at least one, given 30+29+13