I did some math and i got this 
x = -2 
 
        
                    
             
        
        
        
Is there any way you could provide more information, a picture or something could be really helpful.
        
             
        
        
        
Answer:
no solutions
Step-by-step explanation:
3(-n+4)+5n=2n
Distribute
-3n +12 +5n = 2n
2n+12 = 2n
Subtract 2n from each side
12 = 0
This is never true so there are no solutions
 
        
                    
             
        
        
        
Look at the graph at which x=3, then look and see what value y is and that will give you f(3).