Answer:
15
Step-by-step explanation:
The factors of 75 are: 1, 3, 5, 15, 25, 75
The factors of 90 are: 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90
The factors of 120 are: 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 30, 40, 60, 120
The greatest common factor is 15.