Answer:
All numbers can be written as a product of the prime numbers that conform them.
A) Find two numbers with a common factor of 3 only.
for example:
2*3 = 6
7*3 = 21
Both numbers have the factor 3 in them, and because the other two numbers are primes, we can be sure that the 3 is the only common factor.
B) Write a pair of numbers with a common factor of 2, 3 and 6.
Here we can write:
2*3*2 = 12
3*2*5 = 30
Those two numbers have the common factors 6, 2 and 3.
C) Write a pair of numbers with common factors of 3, 6 and 9.
3*2*3 = 18 (has the factors 2, 3, 3*2 = 6, 3*3 = 9)
-3*2*6 = -36
Both have the common factors 3, 6 and 9 (and they share more common factors like 2, this happens because 6 = 3*2, so if 6 is a common factor, 2 also must be)