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
Solve for x:
1.
4x - 7 = 3
Add 7 to both sides
4x = 10
Divide both sides by 4
x = 10/4
Simplify:
x = 5/2
Answer for question 1: x = 5/2
2.
13 + 2x/3 = 15
Multiply both sides by 3
39 + 2x = 45
Subtract 39 from both sides
2x = 6
Divide both sides by 2
x = 3
Answer for question 2: x = 3
3.
10x + 7 = 15
Subtract 7 from both sides
10x = 8
Divide both sides by 10
x = 8/10
Simplify
x = 4/5
Answer for question 3: x = 4/5
Step-by-step explanation:
Exponential function is given by general form 
Where a and b are constants.
say a=1 and b=2 then we can write function as :

or 
To graph this or any exponential function, we just need to find some points then join them by a curved line.
Like plug x=0, 1, 2,... into above function and find points:
plug x=1

Hence point is (1,2)
Find more points similarly then graph them to get the graph as shown below:
the standard form is 83,902 & the expanded form is 83,000+900+2