Answer:
8
Explanation:
If a sum of a number and 9 is 17 that means that a number plus 9 equals 17 you could write this out in mathematical form as
x + 9 = 17
You probably don't have to use algebra to solve this but I'll show you how just in case
subtract 9 from both sides
x + 9 = 17
-9 -9
x = 8
this is your solution, hope this helped :)