What is the nth term of 20 29 38 47?

We note that there are a difference of '9' between terms . Hence '9n'

Next find the constant 'c'

1st term ; 9(1) + c = 20 => c = 11

2 nd term ; 9(2) + c = 29 => c = 11

nth term is 9n + 11

e.g.

7th term is 9(7) + 11 = 63 + 11 = 74