First you would do -3(1+2n) via the distributive property.
63=-3(1+2n)
63=-3(1)+(-3)(2n)
63=-3+(-6n) or 63=-3-6n
Then you would isolate the variable by doing the inverse operation. Since it’s a two step, start with the number without the variable(n).
63=-3-6n
+3 +3
66=-6n
Now you work on taking care of the variable with the number attached.
66=-6n
/-6 /-6
-11=n
You get a negative number because a positive multiplied/divided by a negative is a negative.
I hope this helps!