Question

How do you get -n by itself?

Answer 1

if that is n/3, then you would at 10 to both sides of the equation, then multiply everything by 3/1 canceling out the 3 in n/3 and being left with n = 30. 

Answer 2

add 10 to both sides, then multiply by -3 on both sides, so:
-n/3-10=0
-n/3=0+10
-n/3=10
n=10x(-3)
n=-30