Answer
$-4$
Work Step by Step
$d=a_{n+1}-a_{n}=-20-\left( -16\right) =-16-\left( -12\right) =-12-\left( -8\right) =-4$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.