I would set this up as a a proportion:

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 17x = 1360
x = 20 cm
 
        
        
        
According to formula
P(1 - R/100)^ T
P =PRICE
R =RATE OF DEPRECIATION
T= TIME
answer is $47320
        
                    
             
        
        
        
So in this problem we need to do some addition. 
take the starting balance (-200) and add it to the amount you paid back (30) 
-200 + 30 = -170
        
                    
             
        
        
        
X - 6y=18     
2x-3y=9    |*-2
   x -6y=18
-4x+6y=-18
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-3x=0, x=0
2x-3y=9
2*0-3y=9
-3y=9, y=-9/3, y= -3
        
             
        
        
        
Answer:
x = 13
Step-by-step explanation:
call the missing number x
8 - x = - 5                        Subtract 8 from both sides
8-8 - x = -5-8                  Combine
-x = - 13                           Multiply by -1
x = 13