B. (k+10f)(k-5f) you can tell in 2 ways. 1. if the second sign is neg then the signs in the factors are going to be one neg and one positive so that knocks out C and D. Then you look at the second term and since the 5 is positive then the 10 has to be positive so you end up with a positive 5kf.
The second way is to FOIL them out. When you check B you get

combine your like terms and you have your original expression of

Hope that helps
For this case we have that the quotient of 6 and a number, can be expressed as:

Where the variable "x" represents the incognito number.
Now we have that expression is subtracted from 100. Now, we can write the following:

ANswer:
Option A
Answer:
Er... um... huh?
Step-by-step explanation:
Yes it is the same. 1/4 +1/4 = 1/2. so 9/10-1/2=9/10-1/2
P=5000
t=8
r=7%=0.07
n=4
Now all of this have to be substituted to the formula
A=5000(1+0.07/4)^(4*8)=5000(1+0.07/4)³²=8711.07