What is the rule for the sequence corresponding to this series?–4 + –7 + –10 + –13

The terms decrease by 3 each time, so the common difference is –3. An arithmetic sequence has rule aₙ = first term + (n – 1)(common difference); using the first term –4 gives aₙ = –4 + (n – 1)(–3), which is choice B.

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