Answer:they need to buy 27 boxes of plates.
Step-by-step explanation:I do not like expaining things.
The answer is 13/85. You could find out the answer by doing the reprical multiplication.
The formula for N choose K is given as:
C(n, k)= ![\frac{n!}{[k!(n-k)!] }](https://tex.z-dn.net/?f=%20%5Cfrac%7Bn%21%7D%7B%5Bk%21%28n-k%29%21%5D%20%20%7D)
Where,
n is the total numbers.
k is the number of the selected item.
Options C is correct.
Let's say this number is a:
a*(a-9) = 90
a^2-9a-90 = 0
(a-15)(a+6) = 0
a = 15 or a = -6
Therefor a. would be the correct answer :)