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:
The number of bottles Sylvia sold is 6 bottles.