Charlie has the following data:

j 17 1 6 9 5 17 6 8

if the median is 8, which number could j be?

The median is the middle number of a sequence. In order for us to find the median, we need to set up the numbers from least to greatest. I will do that for you.
1, 5, 6, 6, 8, 9, 17, 17 (implied j).
Cross out the smallest number with the largest number until you can no longer do so.
5, 6, 6, 8 ,9, 17, 17, (implied j).
6 ,6 ,8, 9, 17, (implied j).
6, 8, 9, 17, (implied j)
8, 9, (implied j)
9.
Since we were just short, we need to plug in a number that's after 8 for j.
12 can fit, so j can be 12.
I hope this helps!