Which answer describes the type of sequence?
3, 9, 15, 21, , 9, 15, 21,
geometric
neither arithmetic nor geometric
arithmetic

The best and most correct answer among the choices provided by the question is the last choice "arithmetic"

In mathematics, an arithmetic progression (AP) or arithmetic sequence is a sequence of numbers such that the difference between the consecutive terms is constant. For instance, the sequence 5, 7, 9, 11, 13, 15 … is an arithmetic progression with common difference of 2.

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