You project a drawing 7 in. wide and 4 1/2 in. tall onto a wall. The projected image is 27 in. tall. How wide is the projected image?

The answer is:  "Step 3" . 
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Note:  "Step 3"  incorrectly shows:   "−6m + 6m =  −48 − 12n + 4n " .
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{Rather than the correct equation; which is:

   " - 6m + 6m =  - 48 – 12n + 4 + 4n " .}.
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Note of interest:
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Although not asked in the question/problem, let us continue with the correct equation; & to solve for" n ; 
 

" - 6m + 6m =  - 48 – 12n + (4 + 4n) ; 

     →  " 0 = - 48 – 12n + 4 + 4n " ; 
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Combine the "like terms" on the "right hand side of the equation:
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            -48 + 4 = -44 ;

           - 12n + 4n = - 8n ; 
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  → Rewrite the equation:  " 0 = -8n – 44 " ; 

            ↔  " - 8n – 44 = 0 " ; 

Add "44" to each side of the equation; 
  
            →    -8n – 44 + 44 = 0 + 44 ; 

to get:
 
            →    -8n  = 44 ; 

 Now, divide  EACH SIDE of the equation by:  "-8 " ;
  to isolate "n" on one side of the equation; & to solve for "n" ;  

            →    -8n / 8 = 44 / 8 ;

            →     n = 44/8 = (44 ÷ 4) / (8÷4) = 11/2 ;  

n =  ""  ; or, write as:  "5 "  ;  
                                           
                                           or, write as:  " 5.5 " .
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