Respuesta :
Answer:
The numbers increase by 3
Step-by-step explanation:
The difference between all the numbers in the sequence have a gap of 3
9 and 12 --gap of 3
12 and 15--gap of 3
18 and 21--gap of 3
21 and 24--gap of 3
Answer
y=3+ before
Step-by-step explanation:
you add 3 to every number