first combine like terms, let’s look at the equation. 
5n + 3n - n + 5 = 26 
if we combine the like terms we are left with -
7n + 5 = 26
next you want to subtract 5 from both sides of the equation - 
7n + 5 - 5 = 26 - 5
then you want to simply -
7n = 21
7n/7 = 21/7
cancel terms that are both the numerator and denominator & divide the numbers - 
n = 3