Answer:
Twenty-one is a factor of the number because both 3 and 7 are prime factors.
Step-by-step explanation:
32 and 58 are not prime numbers, so we assume your factorization is supposed to be ...
3^2 × 5^8 × 7
Both 3 and 7 are factors, so 3·7 = 21 will be a factor of the number. (Matches the first choice.)
Ninety is not a factor, because 90 is 2×3^2×5 and 2 is not among the factors given.