If the second term of an arithmetic sequence is -2 and the fourth term is 6, find the seventh term

We can find the common difference, d, between terms thusly :

d  =   [ 4th term - 2nd term ] / [4 - 2]  =  [ 6 - -2] / 2   = [8] / 2  = 4

So....the 7th term is given by

6 + 3d  = 

6 +  3(4)  =

6 + 12  =

18