solve for n

2(n - 9) - 1 = 1     Expand

2n -18  - 1  = 1

2n  - 19  = 1

2n  = 20

n = 10

simplify

2n-18-1=1

simplify

2n-19=1

add 19

2n=20

divide by 2

n=10

(I'm new to this, so get a secon opinion:)