Where are the sets? I don't see any...
A factorial of 7 numbers is just multiplying 7 numbers together like this 1*2*3*4*5*6*7, which equals 5040.
If you wanted to get fancy, you could reword the questions and say, "what is the factorial of 5040?" In that case the answer is 1*2*3*4*5*6*7

Solution:
Given data:
and 
To find
:

Distributive property: 



Arrange and add/subtract same powers.


Hence 
Answer:
Since, the raduis is twice the diameter, we divide the diameter by 2 which 4. The radius is 4 km.
C. 54 is the correct answer because it is greater than 26