Observe the given values:
x | y
0 | 9
1 | 6
2 | 3
As can be observed, an increase in one unit in x (that is, 0 to 1, 1 to 2, ...), leads to a reduction in 3 units in y.
So, if x = 3
y = 3 - 0 = 0
x | y
0 | 9
1 | 6
2 | 3
3 | 0
if x = 4
y = 0 - 3 = -3
0 | 9
1 | 6
2 | 3
3 | 0
4 | -3
if x = 5
y = -3 -3 = -6
0 | 9
1 | 6
2 | 3
3 | 0
4 | -3
5 | -6