12.2 Exercise 5

Determine if each sequence is arithmetic. If so, indicate the common difference.

ⓐ $9 , 20 , 31 , 42 , 53 , 64 , \ldots$ ⓑ $12 , 6 , 0 , −6 , −12 , −18 , \ldots$ ⓒ $7 , 1 , 10 , 4 , 13 , 7 , \ldots$