Answer:
The answer is 15
Step-by-step explanation:
adding 3 to y for each time 1 is added to y. since you start with a base of 9, we can conclude this answer by taking 3 times 15, which is 45, then adding 9, which makes 54. Like this:
0 | 9
1 | 12
2 | 15
...
13 | 48
14 | 51
15 | 54