Attached is an assignment I am having trouble with I did problem 1 and 2 but I don't think it right can someone please look at it? This way I can move on to the remainder of problems 1 and 2.

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

Quick! a survey of 57 customers was taken at a bookstore regarding the types of books purchased. the survey found that 33 customers purchased mysteries, 25 purchased science fiction, 18 purchased romance novels, 12 purchased mysteries and science fiction, 9 purchased mysteries and romance novels, 6 purchased science fiction and romance novels, and 2 purchased all three types of books. a) how many of the customers surveyed purchased only mysteries? b) how many purchased mysteries and science fiction, but not romance novels? c) how many purchased mysteries or science fiction? d) how many purchased mysteries or science fiction, but not romance novels? e) how many purchased exactly two types of books?

Can somebody 1. what is the formula for finding the vertical distance between two points on a coordinate plane?