As x is the number of hardback books and y is the number of paperback books
The sum of x and y need to be greather than or equal to 12 (As Anna wanst to purchase at least 12 books)
As y cost $8.00 and x cost $12.00. She needs that the number of hardback books multiplied by 12 sum to the number of paperbacks multiplied by 8 be less than or equal to the amount of money she has ($150).
Then you have:
