Let x = your number. 
x^2 - 21 = 4x. Subtract 4x from both sides.
x^2 - 4x - 21 = 0. Factor. 
(x - 7) (x + 3) = 0. Set each term to 0.
x + 3 = 0. Subtract 3 from both sides. 
x = -3. This is the negative solution. 
Set the other term equal to zero.
x - 7 = 0. Add 7 to each side. 
x = 7. This is the positive solution.
 
        
             
        
        
        
I would say a but not 100% sure.
        
                    
             
        
        
        
Answer: 140 step by step
Step-by-step explanation:
 
        
             
        
        
        
Answer:
We conclude that  the mean nicotine content is less than 31.7 milligrams for this brand of cigarette.
Step-by-step explanation:
We are given the following in the question:  
Population mean, μ = 31.7 milligrams
Sample mean,  = 28.5 milligrams
 = 28.5 milligrams
Sample size, n = 9
Alpha, α = 0.05 
Sample standard deviation, s =  2.8 milligrams
First, we design the null and the alternate hypothesis

We use One-tailed t test to perform this hypothesis.
Formula:

Putting all the values, we have 

Now,  
 
Since,                  
 
We fail to accept the null hypothesis and accept the alternate hypothesis. We conclude that  the mean nicotine content is less than 31.7 milligrams for this brand of cigarette.
 
        
             
        
        
        
Answer:
W=7
Step-by-step explanation: