Answer:
It's C because we are adding a number on the x but here we skip 5 so it's 6, and on y we add 4 up but since we skipped 5 we add 8 and we get 24. 6, 24. You may say "but SpiritBear, 17 plus eight is 25" and that is true, but if you notice the lowest dot actually starts on 5, not 4 making C right.
Hope this helped and wasn't too confusing