Final answer:
Mai earns $76 in a week if she sells 25 books.
Step-by-step explanation:
Mai earns $51 per week working part-time at a book store. She makes $1 more for each book that she sells. The amount, A (in dollars), that Mai earns in a week if she sells b books is given by the following function: A(b) = 51 + b. To find out how much Mai earns in a week if she sells 25 books, substitute b = 25 into the function: A(25) = 51 + 25 = 76.
Therefore, Mai earns $76 in a week if she sells 25 books.