Tell whether the sequence is arithmetic. if it is, what is the common difference? -15, -9, -3, 3, a) yes; 3 b) yes; 5 c) yes; 6my answer d) no

The difference between -15 and -9 is 6 because you add 6 to -15 to get -9.  The difference between -9 and -3 is also 6 because -9+6=-3.  -3+6=3 also uses the number 6.
It is arithmetic because addition is applied.
You are correct.  The answer is C.

The answer is something i don’t know