Question

What is the next number in the sequence??

Answer 1

Each number is the result of subtracting 12 from the number before, so -9-12 equals -21
The answer B. -21

Answer 2

I'm sure it is B. I have done these kind of questions before.I am a 100%  sure of it. Pls. who knows about my mathlab for free I'm asking for a friend