There are 45 families in a neighborhood, and there are 3 kinds of newspaper—A, B, and
C—that they can subscribe. 27 subscribed A; 18 subscribed B; 12 subscribed C; 9
subscribed A and B; 8 subscribed B and C; 7 subscribed A and C; the number of families
that subscribed all 3 kinds of newspaper is equal to the number of families that
subscribed none of the 3 kinds of newspaper; 39 subscribed at least one kind of
newspaper. How many families just subscribed only one kind of newspaper?
答案：27.0