No. 90 is composite and therefore cannot be a prime factor.
The greatest prime factor of 75 and 90 is: 5
The prime factors of 90 are 2,3,3,5.
If A is a factor of 90, the GCF is A. If A is a multiple of 90, the GCF is 90. If A is co-prime with 90, the GCF is 1.
The prime factor of 19 is 19. The prime factors of 90 are 2, 3 and 5.
3
Five
The prime factors of 70 are 2, 5, and 7. The prime factors of 90 are 2, 3, 3, and 5. The prime factors that 70 and 90 have in common are 2 and 5. The greatest common factor of 70 and 90 is the product of the prime factors they have in common, so it is 2 x 5 = 10.
170
If 21 is a multiple of the number, the number cannot have 90 as a factor.
11 is not a factor of 111.
It is not possible to give a sensible answer to this question. The highest common factor (HCF) refers to a factor that is COMMON to two or more numbers. You have only one number in the question!