Answer:
Step-by-step explanation:
The given equation is
[tex]0.60(x + 38 000) = 51 000[/tex]
Where [tex]x[/tex] represents the number of hardcover books sold. To find the answer we just have to isolate the variable and solve.
First, we apply distributive property
[tex]0.60x+22800=51000[/tex]
Now, we isolate [tex]x[/tex]
[tex]0.60x=51000-22800\\0.60x=28200\\x=\frac{28200}{0.60}=47000[/tex]
This result means that the author sold 47000 hardcover books, which make him to gain $51000.
Therefore, the answer is 47,000 books.