First you have to isolate the variable. That means you have to get all the terms with the letter (n) on one side of the equal sign and everything else on the other side. To do this:
First add 3n to both sides and get:
15=4n-1
Now you have to add 1 to both side and get:
16=4n
Now you have to divide both sides by 4.
You get the answer of:
4=n
