If the number is N, 8 times the number is 8N.
The sum of the number and 9 is (N+9).
When 8 times the number is added to the sum of the number and 9, you have
8N + N + 9
This can be simplified to
9N + 9
And factored to
9(N+1)
The sum of the number and 9 is (N+9).
When 8 times the number is added to the sum of the number and 9, you have
8N + N + 9
This can be simplified to
9N + 9
And factored to
9(N+1)