Complete the square to solve 4x^2+24x=4.

we are given

We can see that left side is multiple of 4

so, we can factor out 4

we can cancel 4

now, we can complete square

now, we can take sqrt

we will get two equations

first equations:

Second equation:

so, we will get solution as

.............Answer

4x^2+24x=4

Step 1:

make the coefficient of x² as 1, divide both sides by 4

x² +6x =1

Step 2:

take half of coefficient of x, square it and add it to both sides

half of 6 is 3 and 3²=9, so add 9 to both sides

x² +6x+9=1+9

x²+6x+3²=10

(x+3)²=10

now when we take square root we will get both + and - √10 on right side

x+3= +√10

x+3=-√10

solving for x

x=+√10-3

x=-√10-3

You do not have to worry about permutation (counting 2 or more possibilities multiple times) as the positions are unique. 

So you can think of these kind of questions step by step. 
1st step: 
How many ways can you fill the 1st position? (cook)
8 candidates, this 8 ways

2nd step: 
For 8 different cooks how many food servers can be selected?
As a persion cannot be cook and server for any cook selected there are 7 different people who can be servers, so this is 8*7 ways

3rd step: 
For all the 8*7 ways of cooks there are 6 people who can be cashiers. 

So the solution is: 8*7*6=336