I think it is 6 (Would be 6/9)
4/5 - ?/9 = 6/45
Make the denominators the same
4/5 (9/9) = 36/45
?/9 (5/5) = ?/45
To get the number, you take 6 from 36 to get 30. And to check, 36-30=6.
Now the fraction is 30/45 and you divide both numbers by 5 to get back to the previous number which would be 45/5 = 9 and 30/5 = 6 which gets you 6/9
