Note the equal sign. What you do to one side, you do to the other. Isolate the variable (n). Do the opposite of PEMDAS.
Subtract 3 from both sides
6n + 3 (-3) = 2 (-3)
6n = -1
Divide 6 from both sides
6n/6 = -1/6
n = -1/6
-1/6 is your solution.
hope this helps