Answer this question too for 30 points and

The author must sell 300 books.

Step-by-step explanation:

The total amount earned  = advance + books sold * money per book

We know they want to make 7000

The advance is 2500

They earn 1.50 for each book sold

b= number of books sold

Substituting in

7000= 2500 + 1.5b

Subtract 2500 from each side

7000-2500 = 2500-2500 + 1.5 b

4500 = 1.5 b

Divide each side by 1.5

4500/1.5 = 1.5b/1.5

3000 = b

the difference is 150 but them total is 950