The nth term is a function so you can do the same thing as you would do with e.g. f (n ) .SO Whereever in the formula we see an n we just make that 2n or 2n-1?
If the nth term is 3n+2 then you can write f(n )=3n+2.
Then e.g. the 4th term is f(4)=3(4)+2 = 14
And e.g. the (n+2)th term is f(n+2) = 3(n+2) + 2 = 3n+8