How many ways can you stack 77 books into equal piles

Ineed to learn how to solve this problem

Over the course of the school year, you keep track of how much snow falls on a given day and whether it was a snow day. your data indicates that of twenty-one days with less than three inches of snow, five were snow days, while of the eight days with more than three inches of snow, six were snow days. if all you know about a day is that it is snowing, what is the probability that it will be a snow day?

Perry observes the opposite parallel walls of a room in how many lines do the plains containing the walls intersect