You can put this solution on YOUR website! first you subtract 4n from both sides of the equation
3n-7-4n=4n+5-4n
then collect and cancel the terms
-n-7=5
now add 7 to both sides of the equation
-n-7+7=5+7
-n=12
now to get n you just have to switch the signs
n= -12
I hope this helps
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