25 has 3 factors: 1, 5 and 25. Only those 3 numbers can be evenly divided into 25. 1 is a factor for every number, 5 can be divided into 25, 5 times and a number is always a factor of itself as well.
So just find the factors of 90
90=2 times 3 times 3 times 5
so the factors could be
2,3,15
2,9,5
6,3,5
10,3,3
there are 4our
The answer is B because the first number in those points don’t repeat but all the other ones have the first number repeating
Answer:
It's the 3rd one using the formula 
Once you follow that step you need to multiply the exponent of 3 and 6 with the exponent outside the parenthesis..... which is why it's the 3rd one.