Answer:
C
Step-by-step explanation:
look up rules of multiplying radicals.
You can multiply the radicands (the number inside the square root) then take the square root of the new number.
3*21 = 63
Factor 63 into 3*3*7
Pull out 3^2 from inside the square root
leaves you with 3sqrt7 or answer C
Answer: Her e-mail password is 
Step-by-step explanation:
You know that a part of Rivka's e-mail password is formed by the last four digits of her telephone number.
The exercise gives you the last four digits of Rivka's telephone number:

Now, in order to find the other numbers, you need to descompose
into its prime factors. Then:

Therefore, based on this, you can determine that her e-mail password is:

18.9 rounded is 19
5.2 rounded is 5
19 * 5 = 95
It's suppose to be -18 so I guess no real number....