Interesting logical problem

[kate]

How many people leave in one building, which has three four-leveled parts, if we know that:

a) in part A are living 39 people more that those in part B, but 77 people less that those in part C;
b) in every 13 children, there are 7 students;
c) for New Year the housekeeping council bought 1400 greeting cards, and with more than the half of which greeted the inhabitants of the neighboring building, and with the rest - the people from this building - 1 card per person;
d) the adults are 20% more than the children;
e) if on the first floors move 17 new people, and from the second floors 11 people move to the third ones, and from the forth floors 15 people leave, than on every floor there will be equal number of people.