All you need to do is make a tape diagram.
Now, count up how many celery sticks there are.
For example: if you have 4, keep adding 4 until you fill the diagram.
So it would look like this:
Celery: 1, 2, 3, 4, 5, 6, 7, 8 (Or however many of these you have to start with)
Carrot: 4, 8, 12, 16, 20, 24, 28, 32
Tomatoes: 3, 6, 9, 12, 15, 18, 21, 24
So in conclusion: Alejandro will use 8 celery sticks and 24 cherry tomatoes if he uses 32 carrot sticks.