Answer:
option C. 
Step-by-step explanation:
we know that
The volume of the triangular pyramid is equal to

where
B is the area of the triangular base
h is the height of the pyramid
In this problem we have


substitute in the formula

A percentage is a portion out of 100, and because it is a portion of a whole it can be written as a fraction of an amount (in this case a fraction of 100). You can also rewrite this as a decimal because a fraction is essentially the same thing as a division problem and when you divide a number by 100 you usually get a decimal (if the numerator is smaller than 100 that is), and also because decimals are similar to fractions because they represent parts a whole unit for instance the percentage 72% is equivalent to the fraction 72/100 which is the same as 72 divided by 100 which is the same as the decimal 0.72.
Sorry for the long explanation but I hope this helped!
Step-by-step explanation:
a).
n! is

(n-3)! is

If we divide the two, everything behind (n-3) will just cancel out so we would be left with only

So the answer to a is

b
Permutations formula of P(6,4) is
6!/(6-4)!, or 6!/2!.

Then we divide by 4!

The answer to b is 15
Answer is in the attached photo
X=15.6 miles