Answer:
There are three possible arrangements of the graduated  cylinders on the shelf.
1. 4 rows of 9 graduated cylinders
2. 3 rows of 12 graduated cylinders.
3. 2 rows of 18 graduated cylinders.
Step-by-step explanation:
Number of graduated cylinders to put away on the shelf = 36
Maximum number of graduated cylinders that can fit across = 20
Maximum number of graduated cylinders that can fit deep = 4
The teacher  wants each row to have the same number of cylinders.
First option of arrangement:
4 rows of 9 graduated cylinders
It fits across (less or equal to 20) and deep (less or equal to 4)
Total of graduated cylinders used = 36 ( 4 x 9)
Second option of arrangement:
3 rows of 12 graduated cylinders
It fits across (less or equal to 20) and deep (less or equal to 4)
Total of graduated cylinders used = 36 ( 3 x 12)
Third option of arrangement:
2 rows of 18 graduated cylinders
It fits across (less or equal to 20) and deep (less or equal to 4)
Total of graduated cylinders used = 36 ( 2 x 18)
No other arrangement is possible, because a only row of 36 graduated cylinders doesn't fit across or 6 rows of 6 don't fit deep.
