For what value of k will k+9, 2k-1 and 2k+7 are the consecutive terms of an arithmetic progression?

For what value of k will k+9, 2k-1 and 2k+7 are the consecutive terms

1.	For what value of k will k+9, 2k-1 and 2k+7 are the consecutive terms of an arithmetic progression?
Answer» K= +18 ..