Find the value of -7 + (-9) + 11 + 8

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?

Gabrielle's age is two times mikhail's age. the sum of their ages is 84. what is mikhail's age?

60 musicians applied for a job at a music school. 14 of the musicians play both guitar and drums. what is the probability that the applicant who gets the job plays drums or guitar?