How do you solve this 2 step equation: 9+9n=9

Move 9 over to the other side so your equation looks like this:
9n = 9 - 9
Then simplify
9n = 0
n = 0

Step 1: Move all terms not containing n to the right side of the equation.
Since 9 does not contain the variable to solve for, move it to the right side of the equation by subtracting 9 from both sides.

9n = −9+9
9n=-9+9
Add −9 and 9 to get 0.
9n=0

Step 2: Divide each term by 9 and simplify.
Divide each term in 9n = 0 by 9
9n=0 by 9.
9n/9=0/9

Step 3: Reduce the expression by canceling the common factors.
n=0/9
Divide 0 by 9 to get 0.
n=0