Answer :
If the empty suitcase weighs 5.7 pounds and each book weighs 2.4 pounds, the total weight can be written as:
[tex]W=5.7+2.4n[/tex]where n is the number of books.
If the total weight has to be less or equal than 50, we can write:
[tex]\begin{gathered} W\le50 \\ 5.7+2.4n\le50 \\ 2.4n\le50-5.7 \\ 2.4n\le44.3 \\ n\le\frac{44.3}{2.4} \\ n\le18.45 \end{gathered}[/tex]As n<=18.45, we know that Jessie can take up to 18 books, as the number of books is an integer.
We can check if the total weight is under 50 as:
[tex]\begin{gathered} W=5.7+2.4\cdot18 \\ W=5.7+43.2 \\ W=48.9 \end{gathered}[/tex]The inequality is satisfied, and if we add one more book the weight goes to 48.9+2.4=51.3, which is over the limit.
Answer: 18 books.