Answer:
see the explanation
Explanation:
Let
x ---->the number of books she can sell if she comes back on Sunday
y ----> the number of books sold on Saturday
we know that
The number of books sold on Saturday plus the number of books she can sell if she comes back on Sunday must be less than or equal to the initial number of books in the library (30 books)
so
The inequality that represent this situation is
we have
substitute
solve for x
subtract 9 both sides
therefore
The maximum number of books she can sell on Sunday is 21