Answer:
Step-by-step explanation:
The sum of a number and 9 is adding of any variable to 9.
E.g the sum of 8 and 7
8+7=15
We can also have the sum of two unknown numbers, we can let the first number be x and the second number be y, then the sum of the two unknown will be (x+y).
So, let apply this to the question
The sum of a number and 9, since we don't the number, let the number be n, then the sum of the number and 9 will be (n+9)
Then the correct option is B which is n+9
