All you have to do is substitute the values in for y to see if they are true.
0: 9 ≤ 6 - 0 = 9 ≤ 6 (FALSE)
3: 9 ≤ 6 - 3 = 9 ≤ 3 (FALSE)
-3: 9 ≤ 6 - -3 = 9 ≤ 9 (TRUE)
-1: 9 ≤ 6 - -1 = 9 ≤ 7 (FALSE)
-6: 9 ≤ 6 - -6 = 9 ≤ 12 (TRUE)
6: 9 ≤ 6 - 6 = 9 ≤ 0 (FALSE)
-4: 9 ≤ 6 - -4 = 9 ≤ 10 (TRUE)
So, the values that belong to 9 ≤ 6 - y are -3, -4, and -6.
