Heather earns 41 dollars per week working part-time at a book store. She makes one dollar more for each book that she
 sells. The amount, A (in dollars), that Heather earns in a week if she sells b books is given by the following.
 A=41 + b
 How much does Heather earn in a week if she sells 18 books?
 dollars
 x
 ?