The number of books which Mr. Hartzel has now is:
This refers to the use of calculations to solve mathematical problems. There are different ways in which algebra is used and this can include addition, subtraction, division, etc.
With this in mind, we can see that Mr Hartzel had 12 books in his library
Then he got 9 new books and then sold off 6 books.
Therefore, the total number of books which he has now is:
12+9-6= 15 books
Read more about algebra here:
https://brainly.com/question/6143254
