For what value of k will K + 9, took a -1 and took a + 7 are the consecutive term AP

For what value of k will K + 9, took a -1 and took a + 7 are the conse

1.	For what value of k will K + 9, took a -1 and took a + 7 are the consecutive term AP
Answer» For what value of k will k+9, 2k+1 and 2k+7 are the consecutive term AP