5 cm since a pentagon has 5 sides just multiply one side by 5 
1x5=5
 
        
             
        
        
        
A=3 so 8*3=24.......................
        
                    
             
        
        
        
Answer:
Step-by-step explanation:
First you do the parentheses so the -3 x 8n= -24 and -3 x -5= 15
so it will look like this. -24n+15-2n=8n-21
Now combine like terms the -24n-2n.
-26n+15=8n-21 now subtract 8n now it will look like this
-34n+15=-21 now -15 from -21 
-34n=-36
now if you want n by its self divide -34 and -36
 
        
             
        
        
        
Answer:
i79
Step-by-step explanation:
 
        
             
        
        
        
10 because 7 x 3 = 21 and 7 + 3 = 10 so your answer is 10