Sylvia had a case of 24 bottles and she sold x bottles.
The amount she ended up with is (24-x).
Sam had a case of 36 and sells 3x bottles (3 times as Sylvia).
Then, he ended up with (36-3x).
If they ended up with the same amount of bottles, then 24-x = 36-3x.
We can calculate x as:
[tex]\begin{gathered} 24-x=36-3x \\ -x+3x=36-24 \\ 2x=12 \\ x=\frac{12}{2} \\ x=6 \end{gathered}[/tex]The number of bottles Sylvia sold is 6 bottles.