Answer:
288 test tubes
Explanation:
Given,
Total chemistry classes = 3
The number of students in each classes = 24,
So, the total number of students in 3 classes = 3 × 24 = 72,
Also, each student to use 4 test tubes.
Therefore, the number of test tubes in 3 classes = 4 × 72 = 288,
Hence, 288 test tubes are needed in all for her classes.