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
Answer:
Step-by-step explanation:Worked out on paper shown below
Also I recommended a online app called (it has wierd name but it’s helpful for algebra) mathpapa
Also I do math in pen so the last answer is messed up it’s 4c^2d and then the rest of the parentheses.Sorry for that.
Answer:

Step-by-step explanation:
3/4+12/8+3/2+10/8=5
Answer:
w² +9w +20
Step-by-step explanation:
Multiply it out, collect terms, and write as descending powers of w.
(5+w)(w+4) = 5w +5·4 +w² +w·4
= w² +9w +20